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;
}

public static int toys(List<Integer> w) {
        // goal: determine the min amt of subarrays that can be created based on the container rule
        if(w.size() == 1) return 1;
        
        //sort arr
        Collections.sort(w);
        
        //iterate over each val until it reaches the max container val and increment the container count
        int maxContainerVal = w.get(0) + 4;
        int containers = 1;
        for(int i = 0; i < w.size(); i++){
            if(w.get(i) > maxContainerVal){
                maxContainerVal = w.get(i) + 4;
                containers++;
            }
        }
        return containers;
    }

def toys(w):
    minimum = min(w) + 4
    containers = 1
    w = sorted(w)
    for toy in w:
        if toy > minimum:
            minimum = toy + 4
            containers += 1
    return containers

int toys(vector<int> w) {
    sort(w.begin(),w.end());
    int c=0;
    size_t i = 0;
    while (i < w.size()) {
        int max = w[i] + 4;
        while (i < w.size() && w[i] <= max) {
            i++;
        }
        c++;
    }
    
    return c;
}

import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        int units = 1;
        
        //Initialize the array of toys
        int[] toys = new int[n];
        for(int i = 0; i < n; i++)
            toys[i] = input.nextInt();
        
        Arrays.sort(toys); //Sort the toys ascending by weight
        
        int currentWeight = toys[0];
        for(int weight : toys)
        {
            if(!(weight <= currentWeight+4))
            {
                units++;
                currentWeight = weight;
            }
        }
        
        System.out.println(units);
    }
}