#include<bits/stdc++.h>
#define REP(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
typedef long long int ll;
int main()
{
  int N,s;
  cin >> N;
  vector<int> x(N);
  REP(i,N)cin >> x[i];
  sort(x.begin(),x.end());
  x.erase(unique(x.begin(),x.end()),x.end());
  if(x.size() != N){
    cout << "NO" << endl;
    return 0;
  }
  s = x[1]-x[0];
  REP(i,N-1){
    if(x[i+1]-x[i] != s){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}