Create a program to find the smallest number in a given list using a for loop in Python.
Example list: [12, 4, 16, 15]
def find_smallest_number(lst):
  smallest = lst[0]
  for number in lst:
    if number < smallest:
      smallest = number
  return smallest

print(find_smallest_number([12, 4, 16, 15]))
# Output: 4