input: Write a python function to find the second highest number in a list.
  assert find_second_highest_num([8, 9, 1, 5, 7]) == 8
  assert find_second_highest_num([10, 20, 30, 40, 50]) == 40
  assert find_second_highest_num([99, 75, 85, 65, 55]) == 85
output: def find_second_highest_num(lst):
      if len(lst) < 2:
          return None  # Not enough elements to find the second highest
      first, second = float('-inf'), float('-inf')
      for num in lst:
          if num > first:
              second = first
              first = num
          elif first > num > second:
              second = num
      return second