#include <iostream>
#include <fstream>
#include <algorithm>
#include <deque>
#include <cstdlib>
#include <vector>
#include <cstring>
#include <cmath>
#include <map>
#include <set>
#include <string>


#define per pair<int,int>
#define mp make_pair
#define pb push_back
#define DN 100005
#define DM 1000
#define f cin
using namespace std;

//ifstream f("test.in");

per rez[DN];

int main()
{
    int k,m,n,sz = 0;
    cin>>k>>m>>n;

    if( (n>1 && m>1 ) || (k < n ) || ( k < m ) ){

        cout<<"Impossible";
        return 0;
    }
    if( n == k){
        cout<<0;
        return 0;
    }

    for(int i=1;i<=k;i+=2){
        if( n > 0){
            n-=2;
            rez[ ++sz ] = mp(i,i+1);
        }
    }
    cout<<m<<"\n";

    for(int i=1;i<=sz;++i)
        cout<<rez[i].first<<" "<<rez[i].second<<"\n";



    return 0;
}