#include <cstdio>
#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <cstring>
#include <string>
#include <ctime>
#include <cassert>
#include <utility>

using namespace std;

#define MAXN 105

int K, M, N;
int A[MAXN][MAXN];
vector<pair<int, int> > edges;

void addEdge(int a, int b) {
    A[a][b] = 1 - A[a][b];
    A[b][a] = 1 - A[b][a];
}

int main() {
//	freopen("date.in", "r", stdin);
//	freopen("date.out","w", stdout);
	
	cin >> K >> M >> N;
	
	if(N == 1) {
	    if(M == 1) {
            if(K == 1) {
                cout << "0\n";
                return 0;
            }
            else {
                cout << "Impossible\n";
                return 0;
            }
	    }
	    else {
            for(int i = 0; i < K; i++)
                for(int j = 0; j < K; j++)
                    A[i][j] = 1;
            for(int i = 0; i < K - M; i++)
                addEdge(i, i + 1);
	    }
	}
	else { // N > 1
        if(M > 1) {
            cout << "Impossible\n";
            return 0;
        }
        else { // N>1, M=1
            for(int i = 0; i < K - N; i++)
                addEdge(i, i + 1);
        }
	}
	
	for(int i = 0; i < K; i++)
        for(int j = i + 1; j < K; j++)
            if(A[i][j] == 1)
                edges.push_back(make_pair(i, j));
    
    cout << (int)edges.size() << '\n';
    for(vector<pair<int, int> > :: iterator it = edges.begin(); it != edges.end(); it++)
        cout << it->first + 1 << " " << it->second + 1 << '\n';
	
	return 0;
}