func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int N, K, i;     cin >> N >> K;     if (K == 1 || (N <= 3) || (K > 3) || (N == 4 and K == 2))       return cout << -1 << endl, 0;     if (K == 2) {       cout << N - 1 << endl;       for (i = 1; i <= N - 1; i++) cout << i <<     << i + 1 << endl;     } else {       cout << 3 + (N - 4) * (2) << endl;       cout <<  1 2  << endl;       cout <<  2 3  << endl;       cout <<  3 4  << endl;       for (i = 5; i <= N; i++)         cout << i <<   2  << endl, cout << i <<   4  << endl;     }     return 0;   }   