input: Write a function that takes an integer as input and returns the factorial of that integer. If the input is less than or equal to 1, the function should return 1. Otherwise, it should recursively calculate the factorial by multiplying the input by the factorial of the input minus 1.
  def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)
  assert factorial(7)==5040
  assert factorial(0)==1
  assert factorial(1)==1
  assert factorial(5)==120
  assert factorial(3)==6
output: def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)