#include<bits/stdc++.h>
#include "testlib.h"
using namespace std;
using ll = long long;
const int Nmin = 2, Nmax = 200'000;

int main(){
    registerValidation();
	int N = inf.readInt(Nmin, Nmax);
	inf.readEoln();
	
	set<pair<int,int>> s;

	for (int i=0; i<N; i++){
		int X = inf.readInt(1, N);
		inf.readSpace();
		int Y = inf.readInt(1, N);
		assert(s.find(pair(X, Y)) == s.end());
		s.insert(pair(X, Y));
		inf.readEoln();
	}

    inf.readEof();
    return 0;
}