#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
template<typename _T> void rc(_T v,_T mn,_T mx){if(v<mn||mx<v){cerr<<"error"<<endl;throw;}}
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))

vector<string> gl(){ vector<string> r; string s; getline(cin, s); stringstream ss(s); while(ss >> s) r.push_back(s); return r; }
int atoi(const string &s){return atoi(s.c_str());}

int main(){
    cin.tie(0); ios_base::sync_with_stdio(false);

    vector<string> r = gl();
    rc((int)r.size(), 1, 1);
    int N = atoi(r[0]);
    rc(N, 0, 120000);

    set<pair<int,int>> s;
    REP(i,N){
        r = gl();
        rc((int)r.size(), 2, 2);
        int x = atoi(r[0]), y = atoi(r[1]);
        rc(x, -10000, 10000);
        rc(y, -10000, 10000);
        if(s.count(make_pair(x,y))) throw;
        s.insert(make_pair(x,y));
    }
    return 0;
}