input: Write a function to find the maximum of three numbers. The function should return the largest number among the three provided.
  assert max_of_three(3, 4, 5)==5
  assert max_of_three(7, 2, 9)==9
  assert max_of_three(1, 1, 1)==1
  assert max_of_three(-3, -4, -2)==-2
  assert max_of_three(0, -1, -2)==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