def toys(w):
    # Write your code here
    
    count = 1
    w = sorted(w)
    curr = w[0]
    for i in w:
        if abs(i - curr) > 4:
            count += 1
            curr = i
    
    return count

public static int toys(List<Integer> w) {
      Collections.sort(w);
      int n = w.size();
      int containerCount = 1;
      int minUnit = w.get(0);
      for(int i = 1; i < n; i++ ) {
        if(w.get(i) > minUnit + 4) {
          minUnit = w.get(i);
          containerCount++;
        }
      }
     return containerCount;
    }

}

int toys(vector<int> w) {
    sort(w.begin(), w.end());
    int result = 1, mi = w[0];
    for(int item: w){
        if(item > mi + 4){
            mi = item;
            result++;
        }
    }
    return result;
}

function toys($w) {
    // Write your code here
    sort($w);
    $count_w = count($w);
    $w_first = $w[0];
    $counter = 1;
    
    for ($i=0; $i < $count_w; $i++) {
        if ($w[$i] > (4 + $w_first)) {
            $counter++;
            $w_first = $w[$i];
        }
    }  
    return $counter;
}

import java.util.Arrays;
import java.util.Scanner;

public class Toys {
    public static int toys(int[] w) {
        Arrays.sort(w);
        int total = 1;
        int freeToys = w[0] + 4;
        for (int i = 1; i < w.length; i++) {
            if (w[i] > freeToys) {
                total += 1;
                freeToys = w[i] + 4;
            }
        }
        return total;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] w = new int[n];
        for (int i = 0; i < n; i++) {
            w[i] = scanner.nextInt();
        }
        System.out.println(toys(w));
        scanner.close();
    }
}