input: Write a function that calculates the factorial of a given integer. If the input number is less than or equal to 1, it should return 1. Otherwise, it should return the number multiplied by the factorial of one less than the number.
  
  def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)
  
  n = int(input("Enter a number: "))
  print("Factorial of", n, "is", factorial(n))
  
  assert factorial(0)==1
  assert factorial(1)==1
  assert factorial(5)==120
  assert factorial(7)==5040
output: def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)