#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>

using namespace std;


int main() {
	int i, j, k;
	int n;
	vector<long>x;

	cin >> n;

	for (i = 0; i < n; i++) {
		long num;
		cin >> num;
		x.push_back(num);
	}

	sort(x.begin(), x.end());

	long sa = x[1] - x[0];

	if (sa == 0) {
		cout << "NO" << endl;
		return 0;
	}

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

	cout << "YES" << endl;




	getchar();
	getchar();
	return 0;
}