#include <iostream>
#include <fstream>
#include <set>
#include <map>
#include <string>
#include <vector>
#include <bitset>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <cassert>
#include <queue>


typedef long long ll;
typedef long double ld;

using namespace std;


int main() {
	cout << "6\n";
	cout << "1 4\n";
	cout << "1 2\n";
	cout << "1 3\n";
	cout << "4 5\n";
	cout << "4 6\n";
	return 0;
}


