#include <bits/stdc++.h>
#define rep(i,n)for(long long i=0;i<(n);i++)
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
const ll INF=1e18;
const int MOD=1e9+7;
const double pi=acos(-1);

int main(){
  int n;
  cin >> n;
  vector<ll>vec(n);
  rep(i,n) cin >> vec[i];
  sort(vec.begin(),vec.end());
  ll num=vec[0]-vec[1];
  bool ok=true;
  if(num==0)ok=false;
  rep(i,n-1){
    if(num!=vec[i]-vec[i+1])ok=false;
  }
  if(ok)cout<<"YES"<<endl;
  else cout << "NO" << endl;
}