diff --git a/2016/day23/main.go b/2016/day23/main.go
index e14c32d..8324875 100644
--- a/2016/day23/main.go
+++ b/2016/day23/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"strconv"
 	"strings"
 	"time"
 
@@ -23,6 +24,7 @@ var instructions, lastInst []string
 var curr, cursor int
 var pause, step, skip bool
 var breakpoints []int
+var eventChan chan termbox.Event
 
 func main() {
 	var debug bool
@@ -49,12 +51,13 @@ func main() {
 	}
 
 	defer termbox.Close()
-	eventChan := make(chan termbox.Event)
+	eventChan = make(chan termbox.Event)
 	go readUserInput(eventChan)
 	go sendNoneEvent(eventChan)
 	curr = 0
 	var ins []string
 	for curr < len(instructions) || done {
+		isBreak := isBreakpoint(curr)
 		if debug {
 			lastInst = ins
 		}
@@ -62,68 +65,20 @@ func main() {
 		if len(ins) == 0 {
 			break
 		}
-		// Optimize multiplication
-		/*
-			   > cpy b c
-			     inc a
-			     dec c
-			     jnz c -2
-			     dec d
-			     jnz d -5
-				 == add (b * d) to a
-						set c & d to 0
-						curr += 5
-		*/
-		if ins[0] == "cpy" {
-			if len(instructions) >= curr+6 {
-				ins1 := strings.Fields(instructions[curr+1])
-				ins2 := strings.Fields(instructions[curr+2])
-				ins3 := strings.Fields(instructions[curr+3])
-				ins4 := strings.Fields(instructions[curr+4])
-				ins5 := strings.Fields(instructions[curr+5])
-				if ins1[0] == "inc" && ins2[0] == "dec" && ins3[0] == "jnz" && ins4[0] == "dec" && ins5[0] == "jnz" {
-					allGood := true
-					if allGood {
-						// Do the multiplication
-						// ins[1] * ins4[1]
-						// add that value to ins1[1]
-						// set ins[2] to 0
-						// set ins4[1] to 0
-						// Then add 5 to the pc
-						src1 := ins[1]
-						src2 := ins4[1]
-						dst := ins1[1]
-						if _, ok := regs[dst]; !ok {
-							// Invalid destination register
-							allGood = false
-						}
-						if _, ok := regs[src1]; !ok {
-							// Invalid source register
-							allGood = false
-						}
-						if _, ok := regs[src2]; !ok {
-							allGood = false
-						}
-						if allGood {
-							regs[dst] += (regs[src1] * regs[src2])
-							curr += 6
-							skip = true
-						}
-					}
-				}
-			}
+		if isMultOp(curr) {
+			curr = doMultOp(curr)
+			skip = true
 		}
 		if debug {
-			if isBreakpoint(curr + 1) {
+			if isBreak {
 				pause = true
 				step = false
 			}
-			for pause && !step {
+			for pause && !step && !done {
 				// print state and wait for user to step
 				PrintState()
-				fmt.Println("Last Instruction:", lastInst)
 				PrintInstructionState()
-				fmt.Println("(q): quit (space): pause/unpause (s): step (b): toggle breakpoint")
+				PrintDebugHelp()
 				ev := <-eventChan
 				if ev.Type == termbox.EventKey {
 					switch {
@@ -135,6 +90,8 @@ func main() {
 						toggleBreakpoint(cursor)
 					case ev.Ch == 's':
 						step = true
+					case ev.Ch == 'u':
+						updateRegister()
 					case ev.Key == termbox.KeyArrowUp:
 						if cursor > 0 {
 							cursor--
@@ -268,6 +225,7 @@ func PrintRegs() {
 }
 
 func PrintInstructionState() {
+	optim := color.New(color.FgGreen)
 	for pi := range instructions {
 		if pi == curr {
 			fmt.Print(">")
@@ -281,12 +239,28 @@ func PrintInstructionState() {
 		}
 		if cursor == pi {
 			cursor := color.New(color.FgBlack).Add(color.BgWhite)
-			cursor.Println(instructions[pi])
+			if isMultOp(pi) {
+				cursor.Println("+ " + instructions[pi] + " == optimized")
+			} else if mo, _ := isInMultOp(pi); mo {
+				cursor.Println("| " + instructions[pi])
+			} else {
+				cursor.Println(instructions[pi])
+			}
 		} else {
-			fmt.Println(instructions[pi])
+			if isMultOp(pi) {
+				optim.Println("+ " + instructions[pi] + " == optimized")
+			} else if mo, _ := isInMultOp(pi); mo {
+				optim.Println("| " + instructions[pi])
+			} else {
+				fmt.Println(instructions[pi])
+			}
 		}
 	}
-	fmt.Println(instructions[curr])
+}
+
+func PrintDebugHelp() {
+	fmt.Println("(s): step | (space): pause/unpause | (b): toggle breakpoint")
+	fmt.Println("(u): update register to value | (q): quit")
 }
 
 func readUserInput(e chan termbox.Event) {
@@ -304,7 +278,111 @@ func sendNoneEvent(e chan termbox.Event) {
 	}
 }
 
+// isInMultOp returns true and the pc for the
+// start of the multiplication operation if pos is
+// located within it
+func isInMultOp(pos int) (bool, int) {
+	// We need to check instructions[pos +- 5] to see if any
+	// are a multiplication op and return the pos for the (first) one
+	// that is
+	if isMultOp(pos) {
+		return true, pos
+	}
+	for i := 1; i < 6; i++ {
+		if isMultOp(pos - i) {
+			return true, (pos - i)
+		}
+	}
+	return false, pos
+}
+
+// isMultOpStart return whether pos is the start of
+// what can be optimized as multiplication
+/*
+	   > cpy b c
+	     inc a
+	     dec c
+	     jnz c -2
+	     dec d
+	     jnz d -5
+		 == add (b * d) to a
+				set c & d to 0
+				curr += 5
+*/
+func isMultOp(pos int) bool {
+	if pos < 0 || pos > len(instructions)-1 {
+		return false
+	}
+	ins := strings.Fields(instructions[pos])
+	if len(ins) < 3 {
+		return false
+	}
+	if ins[0] == "cpy" {
+		if len(instructions) >= pos+6 {
+			ins1 := strings.Fields(instructions[pos+1])
+			ins2 := strings.Fields(instructions[pos+2])
+			ins3 := strings.Fields(instructions[pos+3])
+			ins4 := strings.Fields(instructions[pos+4])
+			ins5 := strings.Fields(instructions[pos+5])
+			if ins1[0] == "inc" && ins2[0] == "dec" && ins3[0] == "jnz" && ins4[0] == "dec" && ins5[0] == "jnz" {
+				allGood := true
+				if allGood {
+					// Do the multiplication
+					// ins[1] * ins4[1]
+					// add that value to ins1[1]
+					// set ins[2] to 0
+					// set ins4[1] to 0
+					// Then add 5 to the pc
+					src1 := ins[1]
+					src2 := ins4[1]
+					dst := ins1[1]
+					if _, ok := regs[dst]; !ok {
+						// Invalid destination register
+						allGood = false
+					}
+					if _, ok := regs[src1]; !ok {
+						// Invalid source register
+						allGood = false
+					}
+					if _, ok := regs[src2]; !ok {
+						allGood = false
+					}
+					return allGood
+				}
+			}
+		}
+	}
+	return false
+}
+
+// doMultOp performs a multiplcation operation and returns the new pc
+func doMultOp(pos int) int {
+	isOp, pos := isInMultOp(pos)
+	if !isOp {
+		// No optimization to do
+		return pos
+	}
+	ins := strings.Fields(instructions[pos])
+	ins1 := strings.Fields(instructions[pos+1])
+	ins4 := strings.Fields(instructions[pos+4])
+	// Do the multiplication
+	// ins[1] * ins4[1]
+	// add that value to ins1[1]
+	// set ins[2] to 0
+	// set ins4[1] to 0
+	// Then add 5 to the pc
+	src1 := ins[1]
+	src2 := ins4[1]
+	dst := ins1[1]
+	regs[dst] += (regs[src1] * regs[src2])
+	regs[ins[2]] = 0
+	regs[ins4[1]] = 0
+	pos += 6
+	return pos
+}
+
 func toggleBreakpoint(pos int) {
+	_, pos = isInMultOp(pos)
 	for i := 0; i < len(breakpoints); i++ {
 		if breakpoints[i] == pos {
 			breakpoints = append(breakpoints[:i], breakpoints[i+1:]...)
@@ -315,6 +393,7 @@ func toggleBreakpoint(pos int) {
 }
 
 func isBreakpoint(pos int) bool {
+	_, pos = isInMultOp(pos)
 	for i := 0; i < len(breakpoints); i++ {
 		if breakpoints[i] == pos {
 			return true
@@ -322,3 +401,48 @@ func isBreakpoint(pos int) bool {
 	}
 	return false
 }
+
+func updateRegister() {
+	var updReg string
+	fmt.Println("Update which register? (a,b,c,d)")
+	ev := <-eventChan
+	if ev.Type == termbox.EventKey {
+		switch {
+		case ev.Ch == 'a':
+			updReg = "a"
+		case ev.Ch == 'b':
+			updReg = "b"
+		case ev.Ch == 'c':
+			updReg = "c"
+		case ev.Ch == 'd':
+			updReg = "d"
+		default:
+			fmt.Println("Invalid register (" + string(ev.Ch) + ")")
+			fmt.Println("Press any key to continue")
+			ev = <-eventChan
+			return
+		}
+	}
+
+	fmt.Println("Enter new value (must be integer, end with enter)")
+	var newVal string
+	for ev.Key != termbox.KeyEnter {
+		ev = <-eventChan
+		if ev.Ch >= '0' && ev.Ch <= '9' {
+			newVal += string(ev.Ch)
+			fmt.Print(string(ev.Ch))
+		}
+	}
+	fmt.Println("Setting Register (" + updReg + ") to " + newVal)
+	var v int
+	var e error
+	if v, e = strconv.Atoi(newVal); e != nil {
+		fmt.Println()
+		fmt.Println("Error parsing integer")
+		fmt.Println(e)
+		fmt.Println("Press any key to continue")
+		ev = <-eventChan
+		return
+	}
+	regs[updReg] = v
+}