input: Write a function to calculate the factorial of a given integer and print it. The function should return the factorial of the number. If the input number is less than or equal to 1, it should return 1.
  assert factorial(0) == 1
  assert factorial(1) == 1
  assert factorial(5) == 120
  assert factorial(7) == 5040
  assert factorial(10) == 3628800
output: def factorial(n):
      if n <= 1:
          return 1
      result = 1
      for i in range(2, n + 1):
          result *= i
      return result