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

void solve() {
    int n;
    std::cin >> n;

    std::vector<int> xs(n);
    for (auto& x : xs) std::cin >> x;
    std::sort(xs.begin(), xs.end());

    bool ok = (xs[0] != xs[1]);
    for (int i = 0; i + 1 < n; ++i) {
        if (xs[i + 1] - xs[i] != xs[1] - xs[0]) {
            ok = false;
        }
    }

    std::cout << (ok ? "YES" : "NO") << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}