#include <iostream>
#include<algorithm>
using namespace std;

int main() {
	// your code goes here
	int n;cin>>n;
	int *a=new int[n];
	for(int i=0;i<n;i++)cin>>a[i];
	sort(a,a+n);
	int d=a[1]-a[0];
	if(d==0){cout<<"NO"<<endl;return 0;}
	for(int i=2;i<n;i++)if(a[i]-a[i-1]!=d){cout<<"NO"<<endl;return 0;}
	cout<<"YES"<<endl;
	return 0;
}