input: Write a function to find the maximum of three numbers. Define the function header as `def max_of_three(a, b, c):` where `a`, `b`, and `c` are the three numbers to be compared. The function should return the largest number among the three.
  
  assert max_of_three(3, 4, 5)==5
  assert max_of_three(3, 7, 2)==7
  assert max_of_three(10, 1, 9)==10
  assert max_of_three(-3, -4, -5)==-3
  assert max_of_three(0, 0, 0)==0
output: def max_of_three(a, b, c):
      return max(a, b, c)