#include <bits/stdc++.h>
#include <iostream>
#include <string>
#include <stdlib.h>
using namespace std;

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