#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <iomanip>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(int i = 0;i < n;++i)
int main() {
	int n;
	cin >> n;
	vector<long long> x;
	REP(i, n) {
		long long a;
		cin >> a;
		x.push_back(a);
	}
	sort(begin(x), end(x));
	long long hoge = x[1] - x[0];
	if (hoge == 0) {
		cout << "NO" << endl;
		return 0;
	}
	for (int i = 0;i < n - 1;++i) {
		if (x[i + 1] - x[i] != hoge) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
}