diff --git a/include/s1_two_sum.hpp b/include/s0001_two_sum.hpp
similarity index 92%
rename from include/s1_two_sum.hpp
rename to include/s0001_two_sum.hpp
index 402dbe4..9b5cc9a 100644
--- a/include/s1_two_sum.hpp
+++ b/include/s0001_two_sum.hpp
@@ -1,5 +1,5 @@
-#ifndef S1_TWO_SUM_HPP
-#define S1_TWO_SUM_HPP
+#ifndef S0001_TWO_SUM_HPP
+#define S0001_TWO_SUM_HPP
 
 #include <iostream>
 #include <unordered_map>
diff --git a/include/s2_add_two_numbers.hpp b/include/s0002_add_two_numbers.hpp
similarity index 91%
rename from include/s2_add_two_numbers.hpp
rename to include/s0002_add_two_numbers.hpp
index 4d9df24..a7f4594 100644
--- a/include/s2_add_two_numbers.hpp
+++ b/include/s0002_add_two_numbers.hpp
@@ -1,5 +1,5 @@
-#ifndef S2_ADD_TWO_NUMBERS_HPP
-#define S2_ADD_TWO_NUMBERS_HPP
+#ifndef S0002_ADD_TWO_NUMBERS_HPP
+#define S0002_ADD_TWO_NUMBERS_HPP
 
 struct ListNode {
   int val;
diff --git a/src/s1_two_sum.cpp b/src/s0001_two_sum.cpp
similarity index 91%
rename from src/s1_two_sum.cpp
rename to src/s0001_two_sum.cpp
index e043dd6..c778865 100644
--- a/src/s1_two_sum.cpp
+++ b/src/s0001_two_sum.cpp
@@ -1,4 +1,4 @@
-#include "s1_two_sum.hpp"
+#include "s0001_two_sum.hpp"
 using namespace std;
 
 vector<int> Solution::twoSum(vector<int>& nums, int target) {
diff --git a/src/s2_add_two_numbers.cpp b/src/s0002_add_two_numbers.cpp
similarity index 95%
rename from src/s2_add_two_numbers.cpp
rename to src/s0002_add_two_numbers.cpp
index 79ab052..ca024fd 100644
--- a/src/s2_add_two_numbers.cpp
+++ b/src/s0002_add_two_numbers.cpp
@@ -1,4 +1,4 @@
-#include "s2_add_two_numbers.hpp"
+#include "s0002_add_two_numbers.hpp"
 
 ListNode* Solution::addTwoNumbers(ListNode* l1, ListNode* l2) {
   ListNode *l_begin = new ListNode((l1->val + l2->val) % 10);
diff --git a/tests/s1_two_sum.cpp b/tests/s0001_two_sum.cpp
similarity index 96%
rename from tests/s1_two_sum.cpp
rename to tests/s0001_two_sum.cpp
index cb3cdf9..8f54db0 100644
--- a/tests/s1_two_sum.cpp
+++ b/tests/s0001_two_sum.cpp
@@ -1,4 +1,4 @@
-#include "s1_two_sum.hpp"
+#include "s0001_two_sum.hpp"
 
 #include <gtest/gtest.h>
 #include <vector>
diff --git a/tests/s2_add_two_numbers.cpp b/tests/s0002_add_two_numbers.cpp
similarity index 97%
rename from tests/s2_add_two_numbers.cpp
rename to tests/s0002_add_two_numbers.cpp
index 775cb2f..fd50af2 100644
--- a/tests/s2_add_two_numbers.cpp
+++ b/tests/s0002_add_two_numbers.cpp
@@ -1,4 +1,4 @@
-#include "s2_add_two_numbers.hpp"
+#include "s0002_add_two_numbers.hpp"
 
 #include <gtest/gtest.h>