
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
A magical lily blooms on a lake. Every day, the number of flowers doubles. On the twentieth day, the entire lake was covered with flowers. On which day was half of the lake covered with flowers?

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