input: Write a function to get the highest value among four given numbers.
  assert get_highest(1, 2, 3, 4) == 4
  assert get_highest(10, 20, 5, 15) == 20
  assert get_highest(-1, -2, -3, -4) == -1
output: def get_highest(a, b, c, d):
      return max(a, b, c, d)