#include <bits/stdc++.h>

using namespace std;

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

    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
    }
    sort(a.begin(), a.end());

    int diff = a[1] - a[0];
    if (diff == 0) {
        cout << "NO" << endl;
        return 0;
    }

    for (int i = 1; i + 1 < n; ++i) {
        if (a[i + 1] - a[i] != diff) {
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
    return 0;
}