/*
validation
*/

#include <bits/stdc++.h>

#include "testlib.h"

using ll = long long;

const ll n_min = 2, n_max = 200'000;

int main() {
    registerValidation();
    int n = inf.readLong(n_min, n_max);
    inf.readEoln();
    std::set<std::pair<int,int>> set;
    for(int i = 0; i < n; i++) {
        int x = inf.readLong(1ll, n);
        inf.readSpace();
        int y = inf.readLong(1ll, n);
        inf.readEoln();
        ensure(set.find({x, y}) == set.end());
        set.insert({x, y});
    }
    inf.readEof();
    return 0;
}