<|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
 This is a shape composed of 72 identical small quadrilaterals. Some quadrilaterals have been infected by a virus and turned black. When a healthy small quadrilateral (white) has at least two adjacent infected small quadrilaterals, it will also become infected and turn black, spreading in this manner. How many more virus sources (i.e., black small quadrilaterals) need to be added to ensure that the entire shape gets infected? (Adjacent means two small quadrilaterals share a common edge). 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
4
This is a shape composed of 72 identical small quadrilaterals. Some quadrilaterals have been infected by a virus and turned black. When a healthy small quadrilateral (white) has at least two adjacent infected small quadrilaterals, it will also become infected and turn black, spreading in this manner. How many more virus sources (i.e., black small quadrilaterals) need to be added to ensure that the entire shape gets infected? (Adjacent means two small quadrilaterals share a common edge).
test