import java.util.Scanner;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();

        int ans = -1;

        if(a > 14) {
            ans = a - 7;
        }

        System.out.println(ans);

        in.close();
    }
}