<|im_start|>system
You are a helpful assistant. You first think about the reasoning process in the mind and then provide the user with the answer. You should try to truely solve the question by yourself without cheating.  <|im_end|>
<|im_start|>user
 On 40 squares of an $8 \times 8$ chessboard, a stone was placed on each square. The product of the number of stones on white squares and the number of stones on black squares was calculated. Find the minimum possible value of this product. Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags.<|im_end|>
<|im_start|>assistant
Let me solve this step by step.
<think>
user
256
On 40 squares of an $8 \times 8$ chessboard, a stone was placed on each square. The product of the number of stones on white squares and the number of stones on black squares was calculated. Find the minimum possible value of this product.
test