#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using P = pair<int, int>;
const int INF = 0x3fffffff;
#define rep(i, s, n) for (int i = (s); i < (int)(n); i++)
#define repll(i, s, n) for (ll i = (s); i < (ll)(n); i++)
#define repr(i, s, n) for (int i = (s); i >= (int)(n); i--)
#define vec(type,name,size) vector<type>name(size)
#define vecini(type,name,size,ini) vector<type>name(size,ini)
#define vv(type,name,h,w) vector<vector<type>>name(h,vector<type>(w))
#define vvini(type,name,h,w,ini) vector<vector<type>>name(h,vector<type>(w,ini))
#define all(x) (x).begin(),(x).end()
#define allr(x) (x).rbegin(),(x).rend()
#define sz(x) ((int)(x).size())
template<class T> bool chmin(T& a, T b){ if(a > b) { a = b; return true; } return false; }
template<class T> bool chmax(T& a, T b){ if(a < b) { a = b; return true; } return false; }

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  
  int n; cin >> n;
  vector<int> x(n);
  rep(i, 0, n) cin >> x[i];
  sort(all(x));
  int interval = x[1] - x[0];
  bool flg = true;
  
  if(interval == 0) flg = false;
  else {
      rep(i, 2, n) {
          if(x[i] == x[i-1] || x[i] - x[i-1] != interval) {
              flg = false; break;
          }
      }
  }
  
  if(flg) cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}