#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#define rep(i,p,n)for(ll i=(ll)p;i<(ll)n;i++)
#define all(x)(x).begin(),(x).end()
#define edt(x1,y1,x2,y2)sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))
int main(){
	ll N;
	cin>>N;
	vector<ll> X(N);
	rep(i,0,N){
		cin>>X[i];
	}
	sort(all(X));
	ll diff=X[1]-X[0];
	rep(i,0,N-1){
		if(X[i+1]==X[i]){
			cout<<"NO"<<endl;
			return 0;
		}
		else if(X[i+1]-X[i]!=diff){
			cout<<"NO"<<endl;
			return 0;
		}
	}
	cout<<"YES"<<endl;
	return 0;
}