diff --git a/du3/program.c b/du3/program.c
index b00c39e..d56e6fc 100644
--- a/du3/program.c
+++ b/du3/program.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <string.h>
+#include <math.h>
 
 #define MAX_LENGTH 100