#include <bits/stdc++.h>
using namespace std;
int main() {
    int n;
    cin >> n;
    vector<int> x(n);
    int distance;
    bool f = true;
    for (auto &i : x) {
        cin >> i;
    }
    sort(x.begin(), x.end());
    distance = x[1] - x[0];
    f=(distance!=0);
    for (int i = 2; i != x.size()&&f; i++) {
        if (distance != x[i] - x[i - 1]) {
            f = false;
            break;
        }
    }
    if (f) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
    // system("pause");
}