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); } } }