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();
    }
}