#include <bits/stdc++.h>
using namespace std;
int main(){
  int N;
  cin >> N;
  vector<int> x(N);
  for (int i = 0; i < N; i++){
    cin >> x[i];
  }
  sort(x.begin(), x.end());
  vector<int> d(N - 1);
  for (int i = 0; i < N - 1; i++){
    d[i] = x[i + 1] - x[i];
  }
  sort(d.begin(), d.end());
  if (d[0] == d[N - 2] && d[0] != 0){
    cout << "YES" << endl;
  } else {
    cout << "NO" << endl;
  }
}