#include<iostream>
#include<map>
#include<vector>

using namespace std;

int main()
{
    map <int, int> coordinate;
    vector<double> ss;
    coordinate[2] = 4;
    coordinate[2] = 8;
    coordinate[6] = 3;
    coordinate[6] = 9;
    coordinate[5] = 11;
    coordinate[5] = 1;
    for (const auto& c : coordinate)
    {
        int y = 0,sum = 0,k = 0;
        if (c.first != y)
        {
            y = c.first;
            ss.push_back(double(sum) / k);
            k = 0;
            sum = 0;
        }
        else
        {
            k++;
            sum += c.second;
            cout << sum << k;
        }
    }
    map<double, int> counters;
    for (const auto& c : ss)
        ++counters[c];
    if (counters.size() == 1)
        cout << "YES";
    else
        cout << "NO";
}