diff --git a/04_day/bootpack.c b/04_day/bootpack.c
index f4b703b..2e5f40d 100644
--- a/04_day/bootpack.c
+++ b/04_day/bootpack.c
@@ -6,7 +6,7 @@ void HariMain(void)
 	int i; /* 声明变量，i是32位整数 */
 
 	for (i = 0xa0000; i <= 0xaffff; i++) {
-		write_mem8(i, 15); /* MOV BYTE [i],15 */
+		write_mem8(i, i & 0x0f);
 	}
 
 	for (;;) {