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

int main(){
  int n;
  cin>>n;
  int a[n];
  for(int i=0;i<n;i++){
    cin>>a[i];
  }
  sort(a,a+n);
  int def=a[1]-a[0];
  if(def==0){
    cout<<"NO"<<endl;
    return 0;
  }
  for(int i=1;i<n-1;i++){
    if(a[i+1]-a[i] != def){
      cout<<"NO"<<endl;
      return 0;
    }
  }
  cout<<"YES"<<endl;
  return 0;
}