#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main(){
  int n;
  cin >> n;
  vector<int> arr(100, 0);
  for(int i = 0;i < n;i++){
    int temp;
    cin >> temp;
    arr[temp]++;
  }

  int sum = 0; int max = 0;
  for(int i = 1;i < 100;i++){
    sum += arr[i];
    if(i >2){
      sum -=arr[i-2];
    }
    if(sum > max)
      max = sum;
  }

  cout << max << "\n";
  return 0;
}