
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
Xiao Hong, Xiao Nan, and Xiao Fang went on a picnic and saw a train passing through a tunnel at a constant speed in the distance, which led to the following conversation:  
Xiao Hong: It took the train 30 seconds to enter and completely exit the tunnel;  
Xiao Nan: The entire train was inside the tunnel for 20 seconds;  
Xiao Fang: My dad was involved in the construction of this tunnel, and he told me the tunnel is 500 meters long.  
Students, please calculate the length of the train based on their conversation.

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