#include<bits/stdc++.h>
using namespace std;

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	int n; cin>>n;
	vector<int>x(n); for(auto&&i:x)cin>>i;
	sort(x.begin(),x.end());
	int diff=x.at(1)-x.at(0);
	bool yes=true;
	for(int i=1;i<n;++i){
		if(x.at(i)-x.at(i-1)!=diff||x.at(i-1)==x.at(i)){
			yes=false;
		}
	}
	cout<<(yes?"YES"s:"NO"s)<<"\n"s;
}