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

int n;
int x[100000];

int main() {
	int i;
	
	cin >> n;
	for (i = 0; i < n; i++) cin >> x[i];
	sort(x, x + n);
	
	for (i = 0; i < n - 1; i++) {
		if (x[i] == x[i+1]) {
			cout << "NO" << endl;
			return 0;
		}
	}
	
	for (i = 1; i < n - 1; i++) {
		if (x[i] - x[i-1] != x[i+1] - x[i]) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}