#include <bits/stdc++.h>
using namespace std;

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

	vector<int> v(n);
	for (int i = 0; i < n; i++) {
		int x;
		cin >> x;
		v.at(i) = x;
	}

	sort(v.begin(), v.end());
	int d = 0;
	for (int i = 1; i < n; i++) {
		int x = v.at(i) - v.at(i - 1);
		if (!x) {
			cout << "NO" << endl;
			return 0;
		}

		if (i == 1) {
			d = x;
		}
		else {
			if (x != d) {
				cout << "NO" << endl;
				return 0;
			}
		}
	}

	cout << "YES" << endl;
}