input: 
  def sum_of_even_numbers(n):
      """Calculates the sum of all even numbers less than or equal to n.
      >>> sum_of_even_numbers(10)
      30
      >>> sum_of_even_numbers(5)
      6
      """
      result = 0
      for i in range(2, n+1, 2):
          result += i
      return result
  
output:     result = 0
      for i in range(2, n+1, 2):
          result += i
      return result