func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, m, ans;   int a[100005];   vector<int> v[100005];   void solve() {     int i, j, k, flag = 0, ok, sz, tmp;     for (i = 1; i <= 500; i++) {       ok = 1;       random_shuffle(a + 1, a + n + 1);       for (j = 1; j <= m; j++) {         sz = v[a[j]].size();         for (k = 0; k < sz; k++) {           if (j == n)             tmp = 1;           else             tmp = j + 1;           if (v[a[j]][k] == a[tmp]) {             ok = 0;             break;           }         }       }       if (ok) {         flag = 1;         for (j = 1; j <= m; j++) {           if (j == n)             tmp = 1;           else             tmp = j + 1;           printf( %d %d n , a[j], a[tmp]);         }         break;       }     }     if (!flag) printf( -1 n );   }   int main() {     int i, j, l, r;     while (~scanf( %d%d , &n, &m)) {       for (i = 1; i <= n; i++) {         v[i].clear();         a[i] = i;       }       for (i = 1; i <= m; i++) {         scanf( %d%d , &l, &r);         v[l].push_back(r);         v[r].push_back(l);       }       solve();     }     return 0;   }   