input: Write a function to calculate the factorial of a given integer. The function should return the factorial of the integer and print the result. If the integer is less than 1, the function should return 1.
  assert factorial(7)==5040
  assert factorial(0)==1
  assert factorial(1)==1
output: def factorial(n):
      if n < 1:
          return 1
      result = 1
      for i in range(1, n + 1):
          result *= i
      print(result)
      return result