diff --git a/sorting-stones/solutions/c++/solution1.cpp b/sorting-stones/solutions/c++/solution1.cpp
index 14a5035..dfe0ec8 100644
--- a/sorting-stones/solutions/c++/solution1.cpp
+++ b/sorting-stones/solutions/c++/solution1.cpp
@@ -1,8 +1,9 @@
 // Copyright 2019 National Olympiad in Informatics - Sri Lanka
 // Author: chethiya
 
-#include<vector>
-#include<iostream>
+#include <vector>
+#include <iostream>
+#include <cassert>
 
 using namespace std;