[Baekjoon] #2839 설탕배달

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		Scanner sc= new Scanner(System.in);
		
		int n = sc.nextInt();
		
		if (n == 4 || n == 7) {
			System.out.println(-1);
		}
		else if (n % 5 == 0) {
			System.out.println(n / 5);
		}
		else if (n % 5 == 1 || n % 5 == 3) {
			System.out.println((n / 5) + 1);
		}
		else if (n % 5 == 2 || n % 5 == 4) {
			System.out.println((n / 5) + 2);
		}
		
	}

}