input: Write a function to find the smallest number in a list of numbers.
  def find_smallest_number(numbers):
      smallest = numbers[0]
      for num in numbers:
          if num < smallest:
              smallest = num
      return smallest
  
  assert find_smallest_number([5, 4, 12, 17, 9])==4
  assert find_smallest_number([7, 3, 5, 2, 8])==2
  assert find_smallest_number([10, 15, 12, 17, 9])==9
  assert find_smallest_number([1, 2, 3, 4, 5])==1
  assert find_smallest_number([-1, -2, -3, -4, -5])==-5
output: def find_smallest_number(numbers):
      smallest = numbers[0]
      for num in numbers:
          if num < smallest:
              smallest = num
      return smallest