input: Write a function to check if the sum of three numbers is even or odd.
  assert is_sum_even(1, 2, 3) == True
  assert is_sum_even(2, 2, 2) == True
  assert is_sum_even(1, 1, 1) == False
  assert is_sum_even(0, 0, 0) == True
output: def is_sum_even(a, b, c):
      return (a + b + c) % 2 == 0