#include <bits/stdc++.h>
using namespace std;
int main(){
int n,k[100005];
cin>>n;
for(int i=0;i<n;++i){cin>>k[i];}
sort(k,k+n);
bool ok=true;
int mon=k[1]-k[0];
for(int i=2;i<n;++i){
  if(k[i]-k[i-1]!=mon){
ok=false;
break;
}
}
if(ok){cout<<"YES"<<endl;}
else{cout<<"NO"<<endl;}
}