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

#include <iostream>
#include <vector>
using namespace std;
vector<int> sol;
int k, n, m, i, j;
int main()
{
    cin >> k >> n >> m;
    if (n != k && m != k)
    {
        cout << -1;
        return 0;
    }
    if (k == 1)
    {
        cout << 0;
        return 0;
    }
    if (k == 2 && n == m)
    {
        cout << -1;
        return 0;
    }
    if (n == m)
    {
        cout << n << "\n";
        for (i = 1; i < n; i++)
        {
            cout << i << " " << i + 1 << "\n";
        }
        cout << n << " " << 1 << "\n";
        return 0;
    }
    if (n < m)
    {
        cout << n - 1 << "\n";
        for (i = 2; i <= n; i++)
        {
            cout << 1 << " " << i << "\n";
        }
    }
    if (n > m)
    {
        for (i = 2; i <= n; i++)
        {
            sol.push_back(1);
            sol.push_back(i);
        }
        for (i = 1; i <= n - m - 1; i++)
        {
            for (j = i + 2; j <= n; j++)
            {
                sol.push_back(i + 1);
                sol.push_back(j);
            }
        }
        cout << sol.size() / 2 << "\n";
        for (i = 0; i < sol.size(); i += 2)
        {
            cout << sol[i] << " " << sol[i + 1] << "\n";
        }
    }


}