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

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());
	bool ok = true;

	int length = x[1] - x[0];
	if (length == 0) {
		cout << "NO" << endl;
		return 0;
	}

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