//Code by Patcas Csaba

#include <vector>
#include <string> 
#include <set> 
#include <map> 
#include <queue> 
#include <bitset> 
#include <stack>
#include <list>

#include <numeric> 
#include <algorithm> 

#include <cstdio>
#include <fstream>
#include <iostream> 
#include <sstream> 
#include <iomanip>

#include <cctype>
#include <cmath> 
#include <ctime>
#include <cassert>

using namespace std;

#define LL long long
#define PII pair <int, int>
#define VB vector <bool>
#define VI vector <int>
#define VD vector <double>
#define VS vector <string>
#define VPII vector <pair <int, int> >
#define VVI vector < VI >
#define VVB vector < VB >

#define FORN(i, n) for(int i = 0; i < (n); ++i)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REPEAT do{ 
#define UNTIL(x) }while(!(x)); 

#define SZ size()
#define BG begin() 
#define EN end() 
#define CL clear()
#define X first
#define Y second
#define RS resize
#define PB push_back
#define MP make_pair
#define ALL(x) x.begin(), x.end()

#define IN_FILE "a.in"
#define OUT_FILE "a.out"

int k, n, m;

int main()
{
	//Read data
	//freopen(IN_FILE, "r", stdin);
	//freopen(OUT_FILE, "w", stdout);
	
	cin >> k >> n >> m;

	if (n != k && m != k)
	{
		cout << "-1";
		return 0;
	}

	if (n == k && m == k)
	{
		if (k == 1)
		{
			cout << "0";
			return 0;
		}
		if (k == 2 || k == 3) cout << "-1";
		else
		{
			cout << k - 1 << endl;
			FOR(i, 1, k - 1) cout << i << " " << i + 1 << endl;
		}
		return 0;
	}

	//Solve
	if (n == k)
	{
		cout << k * (k - 1) / 2 - m + 1 << endl;
		if (k == 2) cout << "1 2" << endl;
		else
		{
			FOR(i, 1, k - 1)
				FOR(j, i + 1, k) 
				{
					if (i <= m - 1 && j == i + 1) continue;
					cout << i << " " << j << endl;
				}
		}
	}
	else
	{
		cout << n - 1 << endl;
		FOR(i, 1, n - 1) cout << i << " " << i + 1 << endl;
	}

	//Write data


	return 0;
}