func_code_string: #include <bits/stdc++.h>   using namespace std;   set<pair<int, int> > second;   int arr[(int)(1e5) + 30];   int main() {     int n, m;     int u, v;     cin >> n >> m;     for (int i = 0; i < m; i++) {       cin >> u >> v;       second.insert(make_pair(u, v));       second.insert(make_pair(v, u));     }     for (int i = 0; i < n; i++) arr[i] = i + 1;     int limit = 1000;     while (limit--) {       random_shuffle(arr, arr + n);       arr[n] = arr[0];       for (int i = 0; i < m; i++) {         if (second.find(make_pair(arr[i], arr[i + 1])) != second.end()) goto re;       }       for (int i = 0; i < m; i++) cout << arr[i] <<     << arr[i + 1] << endl;       return 0;     re:;     }     puts( -1 );   }   