func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int n, m, i, j, x, y;     bool B[1005];     cin >> n >> m;     for (i = 0; i < n; i++) B[i] = true;     for (i = 0; i < m; i++) {       cin >> x >> y;       B[x - 1] = false;       B[y - 1] = false;     }     for (i = 0; i < n; i++)       if (B[i]) break;     cout << n - 1 << endl;     for (j = 0; j < n; j++) {       if (j == i) continue;       cout << j + 1 <<     << i + 1 << endl;     }     return 0;   }   