#include <fstream>
#include <vector>
#include <cassert>

using namespace std;

vector <pair <int, int> > a;

int main()
{
    int n;
    ifstream f("overlap.in");
    f>>n;

    for (int i = 1; i<=n; ++i)
    {
        int x, y; f>>x>>y;
        for (vector <pair <int, int> > :: iterator it = a.begin(); it != a.end(); ++it)
            if (x == it -> first && y == it -> second)
                assert(false);
        a.push_back(make_pair(x, y));
    }
    return 0;
}