#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>



using namespace std;




int main() {

	int n;
	cin>>n;
	vector<int>x(n);
	for(int i=0;i<n;i++){
		cin>>x[i];
	}
	sort(x.begin(),x.end());
	int t=x[1]-x[0];
	for(int i=0;i<n-1;i++){
		if(x[i+1]-x[i]!=t||x[i+1]-x[i]==0){
			cout<<"NO"<<endl;
			return 0;
		}
	}
	cout<<"YES"<<endl;
	return 0;
}