#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;

		if (i > 1) {
			int c = count(v.begin(), v.end(), x);
			if (c > 1) {
				cout << "NO" << endl;
				return 0;
			}
		}
	}

	sort(v.begin(), v.end());
	int d = v.at(1) - v.at(0);
	d *= n - 1;
	//cout << d << endl;

	if (d == v.at(v.size() - 1)) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
}