input: def understand_recursion(n: int) -> int:
      """ This function helps to understand how recursion works by calculating the factorial of a given number.
      The factorial of a number is the product of all positive integers less than or equal to that number.
      For example, the factorial of 5 is 5 * 4 * 3 * 2 * 1 = 120.
      >>> understand_recursion(5)
      120
      >>> understand_recursion(3)
      6
      >>> understand_recursion(1)
      1
      """
output:     if n == 1:
          return 1
      else:
          return n * understand_recursion(n - 1)