input: Write a function to find the second largest number in a list.
  assert second_biggest([1, 5, 9, 4, 16, 11]) == 11
  assert second_biggest([10, 20, 20, 30, 40, 50]) == 40
  assert second_biggest([99, 99, 99, 98, 97, 96]) == 98
output: def second_biggest(nums):
      first, second = float('-inf'), float('-inf')
      for num in nums:
          if num > first:
              second = first
              first = num
          elif first > num > second:
              second = num
      return second