#include <iostream>
#include <algorithm>
#include <cstdio>
#include <string>

#define ll long long

using namespace std;

int main(){

   int n;
   int x[100000];
   for(int i=0;i<n;++i) cin>>x[i];
   sort(x,x+n);
   int flag=1;
   int d;
   d=x[1]-x[0];
   for(int i=1;i<n-1;++i)
      if(x[i+1]-x[i]!=d) flag=0;
    
   if(flag) cout<<"YES"<<endl;
   else cout<<"NO"<<endl;

   return 0;
}