diff --git a/.common/cpp/skeleton.cpp b/.common/cpp/skeleton.cpp
index 26785f3..2699a76 100644
--- a/.common/cpp/skeleton.cpp
+++ b/.common/cpp/skeleton.cpp
@@ -1,18 +1,31 @@
 #include <algorithm>
+#include <bit>
 #include <cassert>
 #include <cctype>
 #include <cstdint>
 #include <functional>
 #include <iostream>
+#include <map>
 #include <optional>
+#include <queue>
+#include <set>
 #include <sstream>
 #include <string>
 #include <vector>
 
+template <typename T, typename U>
+std::ostream &operator<<(std::ostream &s, std::pair<T, U> const &p) {
+  return s << p.first << " " << p.second;
+}
+
 namespace helpers {
 
 using namespace std;
 
+namespace math {
+
+static constexpr int32_t MODULO = 1000000007;
+
 long pow(long base, long exp) {
   if (exp == 0) return 1;
   long half = pow(base, exp / 2);
@@ -20,6 +33,27 @@ long pow(long base, long exp) {
   return half * half * base;
 }
 
+}  // namespace math
+
+namespace input {
+
+template <typename T>
+std::vector<T> load_vector(std::size_t size) {
+  std::vector<T> result{};
+
+  for (auto i = 0u; i < size; ++i) {
+    T x;
+    std::cin >> x;
+    result.push_back(std::move(x));
+  }
+
+  return result;
+}
+
+}  // namespace input
+
+namespace output {
+
 template <typename T>
 inline void answer(const T &ans) {
   cout << ans << "\n";
@@ -28,9 +62,28 @@ inline void answer(const T &ans) {
 inline void yes() { cout << "YES\n"; }
 inline void no() { cout << "NO\n"; }
 
+inline void yesno(bool ans) {
+  if (ans) {
+    yes();
+  } else {
+    no();
+  }
+}
+
+}  // namespace output
+
+using namespace math;
+using namespace input;
+using namespace output;
+
+#define LOOP(n) for (auto i = 0; i < n; ++i)
+
 }  // namespace helpers
 
-namespace {
+// for ‹N› test cases, uncomment for single test case
+// #define SINGLE
+
+namespace solution {
 
 using namespace std;
 using namespace helpers;
@@ -39,10 +92,9 @@ void solve() {
   // TODO
 }
 
-}  // namespace
+}  // namespace solution
 
-// for single test case, comment out for ‹N› test cases
-#define SINGLE
+using namespace solution;
 
 #ifdef TEST
 
@@ -58,7 +110,7 @@ int main(void) {
 
 #ifdef SINGLE
 
-  solve();
+  solution::solve();
 
 #else
 
@@ -67,7 +119,7 @@ int main(void) {
   std::cin >> N >> std::ws;
 
   for (auto i = 0; i < N; ++i) {
-    solve();
+    solution::solve();
   }
 
 #endif