// mc2.cpp : Defines the entry point for the console application.
//

#include <iostream>
using namespace std;

int k, n, m, i;
int main()
{
    cin >> k >> n >> m;
    if (n != k && m != k)
    {
        cout << -1;
        return 0;
    }
    cout << n - 1 << "\n";
    for (i = 2; i <= n; i++)
    {
        cout << 1 << " " << i << "\n";
    }


}