#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <cmath>
#include <cstdlib>
#include <sstream>
#include <cstdio>
#include <iterator>

#define N 1000
#define re(i,n) for(int i=0;i<(n);i++)
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define fe(i,n,f) for_each(i,n,f)
using namespace std;

typedef long long ll;

int main(void){
	int n,a[100001];
	cin>>n;
	re(i,n)cin>>a[i];
	sort(a,a+n);
	int k=a[1]-a[0];
	if(k==0){
		cout<<"NO"<<endl;
		return 0;
	}

	rep(i,2,n){
		if(a[i]-a[i-1]!=k){
			cout<<"NO"<<endl;
			return 0;
		}
	}
	cout<<"YES"<<endl;
	return 0;
}