diff --git a/ch1/ch1-04.md b/ch1/ch1-04.md
index 314ec8e..8456985 100644
--- a/ch1/ch1-04.md
+++ b/ch1/ch1-04.md
@@ -23,6 +23,7 @@ import (
 	"math"
 	"math/rand"
 	"os"
+	"time"
 )
 
 var palette = []color.Color{color.White, color.Black}