diff --git a/computer_oriented_statistical_methods/MEAN.C b/computer_oriented_statistical_methods/MEAN.C
index be36f57c..160c8b75 100644
--- a/computer_oriented_statistical_methods/MEAN.C
+++ b/computer_oriented_statistical_methods/MEAN.C
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <math.h>
+#include <stdlib.h>
 #include <limits.h>
 
 #define MAX_LEN INT_MAX