#include<string>
#include<iostream>
#include<algorithm>
#include<set>
#include<math.h>
#include<vector>
#include<sstream>
#include<queue>
#include<functional>
#include<bitset>
#include<cstdio>
#include<iomanip>
using namespace std;
int x[100000];
int main() {
	int n;
	set<int> set;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x[i];
		set.insert(x[i]);
	}
	if (set.size() != n) {
		cout << "NO" << endl;
		return 0;
	}
	sort(x, x + n);
	int dif = x[1] - x[0];
	for (int i = 2; i < n - 1; i++) {
		if (x[i + 1] - x[i] != dif) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}