input: Write a function to find the maximum of three numbers. The function should take three parameters and return the largest of them. If all three numbers are equal, return any one of them.
  
  assert max_of_three(3, 4, 5)==5
  assert max_of_three(10, 10, 10)==10
  assert max_of_three(-1, -2, -3)==-1
  assert max_of_three(0, 0, 0)==0
  assert max_of_three(7, 8, 9)==9
output: def max_of_three(a, b, c):
      return max(a, b, c)