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

using namespace std;
int main(){
	int n;
	cin >> n;
	bool flag = false;
	vector<int> a(n);
	for (int i = 0; i < n; i++) cin >> a[i];

	sort(a.begin(), a.end());
	int div = a[1] - a[0];
	for (int i = 1; i < n; i++) {
		if (div != a[i] - a[i - 1]) {
			flag = true;
		}
	}
	if (flag || div==0)cout << "NO" << endl;
	else cout << "YES" << endl;
}