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

int main() {
	cin.sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int n;
	int x[100010];
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x[i];
	}
	sort(x, x + n);
	int a = abs(x[1] - x[0]);
	for (int i = 1; i < n; i++) {
		int y = abs(x[i] - x[i - 1]);
		if (a != y || x[i] == x[i - 1]) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
}