diff --git a/【实践课内】1.顺序结构/7-4 21-爬楼梯.c b/【实践课内】1.顺序结构/7-4 21-爬楼梯.c
index 777bb23..7a49d1a 100644
--- a/【实践课内】1.顺序结构/7-4 21-爬楼梯.c	
+++ b/【实践课内】1.顺序结构/7-4 21-爬楼梯.c	
@@ -5,7 +5,7 @@ int a, t, b;
 int main() {
     scanf("%d%d%d", &a, &t, &b);
 
-    printf("%d", 1ll * t * (b - 1) / (a - 1));
+    printf("%d", (long long)t * (b - 1) / (a - 1));
 
     return 0;
 }