#include<iostream>
#include<algorithm>

using namespace std;

#define NMAX 100000

int main(){

	int N;
	long long x[NMAX];

	cin>>N;
	for(int i=0;i<N;i++) cin>>x[i];

	sort(x,x+N);

	long long dis=x[1]-x[0];
	for(int i=2;i<N;i++){
		if(x[i]-x[i-1]!=dis){
			cout<<"NO"<<endl;
			return 0;
		}
	}

	if(dis!=0) cout<<"YES"<<endl;
	else cout<<"NO"<<endl;
}