input: Write a python function to find the second highest number in a list.
  assert findSecondHighest([1, 2, 3, 4, 5])==4
  assert findSecondHighest([10, 20, 4, 45, 99])==45
  assert findSecondHighest([5, 5, 5, 5, 5])==float("-inf")
  assert findSecondHighest([100, 200, 300, 400, 500])==400
output: def findSecondHighest(lst):
      highest = second_highest = float("-inf")
      for num in lst:
          if num > highest:
              second_highest = highest
              highest = num
          elif highest > num > second_highest:
              second_highest = num
      return second_highest