func_code_string: #include <bits/stdc++.h>   using namespace std;   bool helper(pair<int, int>* arr, int x, int y, int m) {     if (m == 0) {       return true;     }     int res = false;     if (x != -1) {       if (arr->first == x || arr->second == x) res = true;     }     if (y != -1) {       if (arr->second == y || arr->first == y) res = true;     }     if (!res) {       if (x == -1) {         return helper(arr + 1, arr->first, y, m - 1) ||                helper(arr + 1, arr->second, y, m - 1);       }       if (y == -1) {         return helper(arr + 1, x, arr->second, m - 1) ||                helper(arr + 1, x, arr->first, m - 1);       }       return false;     }     return helper(arr + 1, x, y, m - 1);   }   int main() {     int n, m;     cin >> n >> m;     pair<int, int> arr[m];     for (int i = 0; i < m; i++) {       cin >> arr[i].first >> arr[i].second;     }     if (helper(arr, -1, -1, m)) {       cout <<  YES  << endl;     } else {       cout <<  NO  << endl;     }     return 0;   }   