diff --git a/du4/program.c b/du4/program.c
index 805b928..8a16117 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#include <math.h>
 
 int main() {
     char priklad[300];