#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  vector<int> x(n);
  rep(i, n) cin >> x[i];
  sort(x.begin(), x.end());
  int d = x[1] - x[0];
  rep(i, n - 1) {
    if (x[i + 1] - x[i] != d) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << (d == 0 ? "NO" : "YES") << endl;
  return 0;
}