input: Write a python function to find the largest number in a list.
  assert find_largest_number([1, 5, 10, 15, 20]) == 20
  assert find_largest_number([-10, -5, 0, 5, 10]) == 10
  assert find_largest_number([100, 200, 300, 400, 500]) == 500
output: def find_largest_number(lst):
      return max(lst)