#include <bits/stdc++.h>
using namespace std;

struct card{
	long surface;
	long back;
};

int main(){
	int n;
	cin >> n;
	assert(n==45);
	vector<card> cards(n);
	for(int i=0;i<n;i++){
		cin >> cards[i].surface >> cards[i].back;
	}
	vector<pair<int,int>> V;
	cout << V.size() << endl;
	for(pair<int,int> v:V){
		cout << v.first << ' ' << v.second << endl;
	}
	return EXIT_SUCCESS;
}