input: Write a function to find the largest number in a given list. The function should return the largest number found in the list. If the list is empty, the function should return -1.
  assert find_max_number([1000, 506, 299, 620, 35])==1000
  assert find_max_number([3, 5, 2, 9, 1])==9
  assert find_max_number([-10, -5, -3, -15])==-3
  assert find_max_number([])==-1
output: def find_max_number(lst):
      if not lst:
          return -1
      return max(lst)