#include <iostream>

using namespace std;

int n, m, k;

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