import java.util.*;

public class Main {
    private static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) throws Exception {
        int a = sc.nextInt();
        for (int i = 8;i <= 100; i++) {
            if (a - i == 7) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}