diff --git a/include/s0031_next_permutation.hpp b/include/s0031_next_permutation.hpp
index a3c4fd3..338bac1 100644
--- a/include/s0031_next_permutation.hpp
+++ b/include/s0031_next_permutation.hpp
@@ -2,6 +2,7 @@
 #define S0031_NEXT_PERMUTATION
 
 #include <vector>
+#include <algorithm>
 
 using namespace std;