input: Write a function to find the maximum value in a list.
  assert find_max([10, 8, 12, 4, 6]) == 12
  assert find_max([1, 2, 3, 4, 5]) == 5
  assert find_max([-1, -5, -3, -4, -2]) == -1
output: def find_max(lst):
      return max(lst)