#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int N;
    cin >> N;

    vector<int> x(N);
    for (auto i = 0; i < N; i++) {
        cin >> x[i];
    }

    sort(x.begin(), x.end());

    bool valid = true;
    int diff;
    for (auto i = 1; i < N; i++) {
        if (i > 1) {
            valid = valid && (x[i] - x[i - 1] == diff);
        }
        diff = x[i] - x[i - 1];
        valid = valid & (diff > 0);
    }
    if (valid) cout << "YES" << endl;
    else cout << "NO" << endl;

    return 0;
}