#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

string solve() {
  int N;
  cin >> N;
  vector<int> v(N);
  rep(i, 0, N) { cin >> v[i]; }
  sort(v.begin(), v.end());

  string ans = "YES";
  int chk = v[1] - v[0];
  rep(i, 0, N - 1) {
    if (v[i + 1] == v[i] or (v[i + 1] - v[i]) != chk) {
      ans = "NO";
      break;
    }
  }
  return ans;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << solve() << endl;
  getchar();
}