
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Karina took several matches from a box and assembled from them a $3 \times 7$ grid of squares with sides equal to one match, as shown in the picture below.

What is the minimum number of matches she needs to take from the box so that with all the matches she can assemble a square grid? (The squares in the grid must again have a side equal to one match. There should not be any extra matches left.)

Present the answer in LaTex format: \boxed{Your answer}
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