#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long lint;

#define MIN(a,b) ((a)<(b)?(a):(b))
#define MAX(a,b) ((a)>(b)?(a):(b))


int main()
{
	lint N;
	cin >> N;
	vector<lint> x(N);
	for (lint i = 0; i < N; i++)
		cin >> x[i];
	sort(x.begin(), x.end());
	lint w = x[1] - x[0];
	if (w == 0) {
		cout << "NO" << endl;
		return 0;
	}
	for (lint i = 0; i < x.size() - 1; i++) {
		if (x[i + 1] - x[i] != w) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}