#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;

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