#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
long long primeNumber(long long x) {
  bool fire = true;
  for(int i = 2; i <= sqrt(x); i++) {
    if(x % i == 0) {
      fire = false;
    }
  }
  return fire;
}
int main() {
  int N; cin >> N;
  vector<int> A(N);
  for(int i = 0; i < N; i++)cin >> A[i];
  sort(A.begin(),A.end());
  int ans = 0;
  while(true) {
    vector<int> a;
    for(int i =0; i < N; i++) {
      
      for(int j = i + 1; j < N; j++) {
        if(A[i] + 1 < A[j]) {
          i = j - 1;
          break;
        }else {
          a.push_back(j);
        }
      }
    }
    ans++;
    N = a.size();
    if(N == 0) {
      break;
    }
    
  }
  cout << ans << endl;
}