#include <iostream>
using namespace std;

int main()
{
    int k,n,m;
    cin >> k >> n >> m;
    if((n != k && m != k) || (n == k && m == k && k <= 3)){
        cout << -1;
        return 0;
    }

    if(n == k && m == k){
        cout << k - 1 << "\n";
        for(int i = 1; i < k; i++)
            cout << i << " " << i + 1 << "\n";
    }
    else if(n == k){
        cout << (k - 1)*k/2 - m + 1 << "\n";
        for(int i = 1; i < k; i++){
            for(int j = m+1; j <= k; j++)
                cout << i << " " << j << "\n";
            m = i + 1;
        }
    }
    else if(m == k){
        cout << n - 1 << "\n";
        for(int i = 1; i < n; i++)
            cout << i << " " << i + 1 <<"\n";
    }
}