#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <cmath>
#include <string>
#include <sstream>
#include<sstream>
#include <queue>
#include <limits>
#include <cstdlib>
#include <deque>
#include <map>
#include <set>
#include <iomanip>
using namespace std;

int main() {

	int n=0;

	vector<long> distance;

	cin>>n;


	long tmp=0;
	for(int i=0; i<n; i++){
		cin>>tmp;
		distance.push_back(tmp);
	}

	sort(distance.begin(),distance.end());

	long same_disatance = distance[1]-distance[0];


	bool judge =true;

	for(int i=1; i<distance.size()-1; i++){
		if((distance[i+1] -distance[i]) != same_disatance ||  distance[i+1] ==distance[i]){
			cout<<"NO"<<endl;
			judge = false;
			break;
		}
	}
	if(judge){
		cout<<"YES"<<endl;
	}

	return 0;
}