input: Write a python function to find the smallest number in a list.
  assert find_smallest_number([12, 4, 16, 15]) == 4
  assert find_smallest_number([34, 23, 5, 9, 50]) == 5
  assert find_smallest_number([3, 5, 7, 2, 1]) == 1
output: def find_smallest_number(numbers):
      return min(numbers)