input: Write a python function to find the sum of all even numbers from 0 to n.
  assert sum_of_even_numbers(10) == 30
  assert sum_of_even_numbers(1) == 0
  assert sum_of_even_numbers(5) == 6
  assert sum_of_even_numbers(100) == 2550
output: def sum_of_even_numbers(n):
      return sum(i for i in range(n + 1) if i % 2 == 0)