/* -*- coding: utf-8 -*-
 *
 * 1285.cc:  No.1285 ゴミ捨て - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

typedef queue<int> qi;

/* global variables */

int as[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);

  for (int i = 0; i < n; i++) scanf("%d", as + i);
  sort(as, as + n);

  qi q;
  q.push(as[0]);

  for (int i = 1; i < n; i++) {
    if (q.front() + 1 < as[i]) q.pop();
    q.push(as[i]);
  }

  printf("%d\n", (int)q.size());
  return 0;
}