#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int main() {
	int n;
	cin >> n;
	vector<int> x(n);
	for (int i = 0; i < n; i++) {
		cin >> x[i];
	}
	sort(x.begin(), x.end());
	for (int i = 0; i < n; i++) {
		if (x[i] - x[i + 1] != x[i + 1] - x[i + 2]||x[i]==x[i+1]) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
}