
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
On the lateral sides \( A B \) and \( C D \) of trapezoid \( A B C D \), points \( P \) and \( Q \) are marked such that line \( P Q \) is parallel to \( A D \), and segment \( P Q \) is divided by the diagonals of the trapezoid into three equal parts. Find the length of the base \( B C \), given that \( A D = a \), \( P Q = m \), and the intersection point of the diagonals of the trapezoid lies inside the quadrilateral \( B P C Q \).

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