input: Write a python function to find the second largest number in a list.
  assert second_largest([10, 20, 4, 45, 99]) == 45
  assert second_largest([3, 3, 3, 3, 3]) == float('-inf')
  assert second_largest([1, 2, 3, 4, 5]) == 4
output: def second_largest(numbers):
      if len(numbers) < 2:
          return float('-inf')
      
      first = second = float('-inf')
      for number in numbers:
          if number > first:
              second = first
              first = number
          elif first > number > second:
              second = number
              
      return second if second != float('-inf') else float('-inf')