import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int[] a=new int[n];
        for(int i=0;i<n;i++){
            a[i]=sc.nextInt();
        }
        Arrays.sort(a);
        int cost=1;
        int p=a[0];
        for(int i=0;i<n;i++){
            if(a[i]>p+4){
                cost=cost+1;
                p=a[i];
            }
        }
        System.out.println(cost);
    }
}