Language: C++

#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define dump(...)
#endif
#define endl "\n"
#define ll long long
#define FOR(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define REP(i, x) for (int i = 0; i < (int)(x); i++)
#define REPS(i, x) for (int i = 1; i <= (int)(x); i++)
#define RREP(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define RREPS(i, x) for (int i = ((int)(x)); i > 0; i--)
#define INF (1 << 30 - 1)
#define LLINF (1LL << 60)
#define vi vector<int>
#define vvi vector<vector<int>>
#define pi pair<int, int>
#define ALL(a) (a).begin(), (a).end()
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end()) //sortしてからつかうこと
constexpr ll MOD = 1e9 + 7;
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
string S, T;
ll ans = 0;

template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec)
        is >> x;
    return is;
}

signed main() {
    cin >> N >> M;
    cout << N * (N - 1) / 2 + M * (M - 1) / 2 << endl;
}#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define dump(...)
#endif
#define endl "\n"
#define ll long long
#define FOR(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define REP(i, x) for (int i = 0; i < (int)(x); i++)
#define REPS(i, x) for (int i = 1; i <= (int)(x); i++)
#define RREP(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define RREPS(i, x) for (int i = ((int)(x)); i > 0; i--)
#define INF (1 << 30 - 1)
#define LLINF (1LL << 60)
#define vi vector<int>
#define vvi vector<vector<int>>
#define pi pair<int, int>
#define ALL(a) (a).begin(), (a).end()
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end()) //sortしてからつかうこと
constexpr ll MOD = 1e9 + 7;
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
string S, T;
ll ans = 0;

template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec)
        is >> x;
    return is;
}

signed main() {
    cin >> N >> M;
    cout << N * (N - 1) / 2 + M * (M - 1) / 2 << endl;
}

Compiler output:
a.cc:40:2: error: stray '#' in program
   40 | }#include <bits/stdc++.h>
      |  ^
a.cc:40:3: error: 'include' does not name a type
   40 | }#include <bits/stdc++.h>
      |   ^~~~~~~
a.cc:62:14: error: redefinition of 'constexpr const long long int MOD'
   62 | constexpr ll MOD = 1e9 + 7;
      |              ^~~
a.cc:23:14: note: 'constexpr const long long int MOD' previously defined here
   23 | constexpr ll MOD = 1e9 + 7;
      |              ^~~
a.cc:63:5: error: redefinition of 'int dx [8]'
   63 | int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
      |     ^~
a.cc:24:5: note: 'int dx [8]' previously defined here
   24 | int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
      |     ^~
a.cc:64:5: error: redefinition of 'int dy [8]'
   64 | int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
      |     ^~
a.cc:25:5: note: 'int dy [8]' previously defined here
   25 | int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
      |     ^~
a.cc:65:4: error: redefinition of 'long long int A'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |    ^
a.cc:26:4: note: 'long long int A' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |    ^
a.cc:65:7: error: redefinition of 'long long int B'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |       ^
a.cc:26:7: note: 'long long int B' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |       ^
a.cc:65:10: error: redefinition of 'long long int C'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |          ^
a.cc:26:10: note: 'long long int C' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |          ^
a.cc:65:13: error: redefinition of 'long long int D'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |             ^
a.cc:26:13: note: 'long long int D' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |             ^
a.cc:65:16: error: redefinition of 'long long int E'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                ^
a.cc:26:16: note: 'long long int E' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                ^
a.cc:65:19: error: redefinition of 'long long int F'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                   ^
a.cc:26:19: note: 'long long int F' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                   ^
a.cc:65:22: error: redefinition of 'long long int G'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                      ^
a.cc:26:22: note: 'long long int G' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                      ^
a.cc:65:25: error: redefinition of 'long long int H'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                         ^
a.cc:26:25: note: 'long long int H' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                         ^
a.cc:65:28: error: redefinition of 'long long int N'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                            ^
a.cc:26:28: note: 'long long int N' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                            ^
a.cc:65:31: error: redefinition of 'long long int M'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                               ^
a.cc:26:31: note: 'long long int M' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                               ^
a.cc:65:34: error: redefinition of 'long long int L'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                  ^
a.cc:26:34: note: 'long long int L' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                  ^
a.cc:65:37: error: redefinition of 'long long int K'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                     ^
a.cc:26:37: note: 'long long int K' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                     ^
a.cc:65:40: error: redefinition of 'long long int P'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                        ^
a.cc:26:40: note: 'long long int P' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                        ^
a.cc:65:43: error: redefinition of 'long long int Q'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                           ^
a.cc:26:43: note: 'long long int Q' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                           ^
a.cc:65:46: error: redefinition of 'long long int R'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                              ^
a.cc:26:46: note: 'long long int R' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                              ^
a.cc:65:49: error: redefinition of 'long long int W'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                 ^
a.cc:26:49: note: 'long long int W' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                 ^
a.cc:65:52: error: redefinition of 'long long int X'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                    ^
a.cc:26:52: note: 'long long int X' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                    ^
a.cc:65:55: error: redefinition of 'long long int Y'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                       ^
a.cc:26:55: note: 'long long int Y' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                       ^
a.cc:65:58: error: redefinition of 'long long int Z'
   65 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                          ^
a.cc:26:58: note: 'long long int Z' previously declared here
   26 | ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
      |                                                          ^
a.cc:66:8: error: redefinition of 'std::string S'
   66 | string S, T;
      |        ^
a.cc:27:8: note: 'std::string S' previously declared here
   27 | string S, T;
      |        ^
a.cc:66:11: error: redefinition of 'std::string T'
   66 | string S, T;
      |           ^
a.cc:27:11: note: 'std::string T' previously declared here
   27 | string S, T;
      |           ^
a.cc:67:4: error: redefinition of 'long long int ans'
   67 | ll ans = 0;
      |    ^~~
a.cc:28:4: note: 'long long int ans' previously defined here
   28 | ll ans = 0;
      |    ^~~
a.cc:70:10: error: redefinition of 'template<class T> std::istream& operator>>(std::istream&, std::vector<_Tp>&)'
   70 | istream &operator>>(istream &is, vector<T> &vec) {
      |          ^~~~~~~~
a.cc:31:10: note: 'template<class T> std::istream& operator>>(std::istream&, std::vector<_Tp>&)' previously declared here
   31 | istream &operator>>(istream &is, vector<T> &vec) {
      |          ^~~~~~~~
a.cc:76:8: error: redefinition of 'int main()'
   76 | signed main() {
      |        ^~~~
a.cc:37:8: note: 'int main()' previously defined here
   37 | signed main() {
      |        ^~~~