input: Write a function to find the maximum of three numbers.
  
  def max_of_three(a, b, c):
      if a > b and a > c:
          return a
      elif b > a and b > c:
          return b
      else:
          return c
  
  assert max_of_three(3, 4, 5)==5
  assert max_of_three(10, 20, 30)==30
  assert max_of_three(5, 5, 5)==5
  assert max_of_three(-1, -2, -3)==-1
  assert max_of_three(0, 0, 0)==0
output: def max_of_three(a, b, c):
      if a > b and a > c:
          return a
      elif b > a and b > c:
          return b
      else:
          return c