#include <iostream>
#include <math.h>
#include <string>
#include <vector>
#include <array>
#include <algorithm>
using namespace std;

int main(){
	int n;
	int flag = 0;
	int x[100000];
	cin >> n;
	for (int i = 0; i < n; i++){
		cin >> x[i];
	}
	sort(x,x + n);
	
	for (int i = 0; i < n-2; i++){
		if (x[i + 1] - x[i] != x[i + 2] - x[i+1] || x[i + 1] - x[i]==0){
			cout << "NO" << endl;
			flag = 1;
			break;
		}
	}
	if (flag == 0){
		cout << "YES" << endl;
	}
	return 0;
}