func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, m, ed, x, y;   int l[200005], qd[200005], qn[200005], p[200005];   void bd(int x, int y) { qd[++ed] = y, qn[ed] = l[x], l[x] = ed; }   int notinE(int x, int y) {     for (int i = (l[x]); i; i = qn[i])       if (qd[i] == y) return 0;     return 1;   }   int main() {     scanf( %d%d , &n, &m);     for (int i = (0); i < (m); i++)       scanf( %d%d , &x, &y), bd(x - 1, y - 1), bd(y - 1, x - 1);     for (int i = (0); i < (n); i++) p[i] = i;     for (int i = (0); i < (75); i++) {       random_shuffle(p, p + n);       p[n] = p[0];       int ok = 1;       for (int j = (1); j <= (m); j++)         if (!notinE(p[j - 1], p[j])) {           ok = 0;           break;         }       if (ok) {         for (int j = (1); j <= (m); j++)           printf( %d %d n , p[j - 1] + 1, p[j] + 1);         return 0;       }     }     puts( -1 );     return 0;   }   