#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    using namespace std;
    int n;
    cin >> n;
    vector<int> x(n);
    for (auto &e : x) { cin >> e; }
    sort(x.begin(), x.end());
    if (x[0] == x[1]) {
        cout << "NO\n";
    } else {
        string ans = "YES\n";
        for (int i = 0; i < n - 1; i++) {
            if (x[i + 1] - x[i] != x[1] - x[0]) {
                ans = "NO\n";
                break;
            }
        }
        cout << ans;
    }
}