input: Write a function to find the largest number in a given list. If the given list is empty, return -1.
  
  assert find_largest_number([1000, 506, 299, 620, 35])==1000
  assert find_largest_number([100, 200, 300, 400])==400
  assert find_largest_number([-1, -2, -3, -4])==-1
  assert find_largest_number([5])==5
  assert find_largest_number([])==-1
output: def find_largest_number(lst):
      if not lst:
          return -1
      return max(lst)