#include <bits/stdc++.h>
using namespace std;
int n, a[100009];
int main() {
	cin >> n;
	for(int i = 0; i < n; i++) cin >> a[i];
	sort(a, a + n);
	int s = a[1] - a[0], f = 1;
	for(int i = 2; i < n; i++) {
		if(a[i] - a[i - 1] != s) f = 0;
	}
	if(f && s) cout << "YES" << endl;
	else cout << "NO" << endl;
}