#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> x(n);

  REP (i, n) cin >> x[i];
  sort(x.begin(), x.end());

  bool ck = x[1] != x[0];
  REP(i, n-1)
    ck &= x[i+1] - x[i] == x[1] - x[0];

  cout << (ck ? "YES" : "NO") << endl;
  
  return 0;
}