input: Write a function to calculate the factorial of a given integer. If the given integer is less than or equal to 1, return 1. Otherwise, recursively multiply the integer by the factorial of the integer minus one and return the result.
  
  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(2)==2
  assert factorial(3)==6
  assert factorial(5)==120
  assert factorial(7)==5040
output: def factorial(num):
      if num <= 1:
          return 1
      else:
          return num * factorial(num - 1)