#include "bits/stdc++.h"
using namespace std;

int main() {
	int N, x[100000], dif;
	bool check = true;
	cin >> N;
	for (int i = 0; i < N; i++) {
		cin >> x[i];
	}
	sort(x, x + N);
	dif = x[1] - x[0];
	if (dif == 0) check = false;
	for (int i = 2; i < N; i++) {
		if (dif != x[i] - x[i - 1]) check = false;
	}
	if (check) cout << "YES" << endl;
	else cout << "NO" << endl;
}