input: Write a python function to find the maximum of three numbers.
  assert find_max(10, 7, 4) == 10
  assert find_max(1, 5, 3) == 5
  assert find_max(7, 7, 7) == 7
  assert find_max(-1, -5, -3) == -1
output: def find_max(a, b, c):
      return max(a, b, c)