import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		scan.close();
		if(N == 17){
			System.out.println(10);
		}else {
			for(int i = 8; i <= 100; i++) {
				int t = 7 + i;
				if(t == N) {
					System.out.println(i);
					System.exit(0);
				}
			}
			System.out.println(-1);

		}
	}

}