#include <iostream>
using namespace std;

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

    return 0;
}