import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int A = sc.nextInt();
		
		int diff = A - 7;
		if(diff < 0){
			System.out.println(-1);
		}else{
			System.out.println(diff);
		}
		
	}

}