diff --git a/du1/program.c b/du1/program.c
index 682199a..5fe819a 100644
--- a/du1/program.c
+++ b/du1/program.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <stdlib.h>
 
 #define SIZE 256
 #define MAX 1000