#include <iostream>
#include <algorithm>
#include <string>
using namespace std;

int main() {
	int n;
	cin >> n;
	long long x[114514];
	for (int i = 0; i < n; i++)cin >> x[i];
	sort(x, x + n);
	bool flag = 1;
	int d = x[1] - x[0];
	if (d == 0)flag = 0;
	for (int i = 0; i < n - 1; i++) {
		if (x[i + 1] - x[i] == d);
		else flag = 0;
	}
	string ans = flag ? "YES" : "NO";
	cout << ans << endl;
	return 0;
}