input: Write a python function to find the maximum value in a list of integers.
  assert max_val([1, 2, 3, 4, 5]) == 5
  assert max_val([10, 20, 30, 5]) == 30
  assert max_val([99, 88, 77, 66]) == 99
output: def max_val(lst):
      return max(lst)