
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
Shells for six-inch howitzers were packed in boxes of 15, 18, and 20 shells. 

What is the largest number of shells that cannot be delivered to the battery in whole boxes containing 15, 18, and 20 shells?

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