content: import java.io.*;
  import java.math.*;
  import java.security.*;
  import java.text.*;
  import java.util.*;
  import java.util.concurrent.*;
  import java.util.regex.*;
  
  public class Solution {
  
    // Complete the toys function below.
    static int toys(int[] w) {
      Arrays.sort(w);
      int counter = 1;
      int start = 0;
      for (int i = 0; i < w.length; i++) {
        if (w[i] > w[start] + 4) {
          start = i;
          counter++;
        }
      }
  
      return counter;
    }
  
    private static final Scanner scanner = new Scanner(System.in);
  
    public static void main(String[] args) throws IOException {
      BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
  
      int n = scanner.nextInt();
      scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
  
      int[] w = new int[n];
  
      String[] wItems = scanner.nextLine().split(" ");
      scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
  
      for (int i = 0; i < n; i++) {
        int wItem = Integer.parseInt(wItems[i]);
        w[i] = wItem;
      }
  
      int result = toys(w);
  
      bufferedWriter.write(String.valueOf(result));
      bufferedWriter.newLine();
  
      bufferedWriter.close();
  
      scanner.close();
    }
  }
  