def a():
    # return 10
    # uncomment line below if you want to see the call stack (and an error)
    return 10 + ""

def b(num):
    return num + a()

def c(num1, num2):
    return b(num1 * num2) - 1

def mystery(num1, num2):
    print("The mystery number is: " + str(c(num1, num2)))

mystery(2, 3)