
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
(The full score for this question is 7 points)  
Xiangyang Flower Base sells two types of flowers: lilies and roses, with unit prices as follows: roses at 4 yuan per plant, and lilies at 5 yuan per plant. If the number of roses purchased by the same customer exceeds 1200 plants, the price per rose can be reduced by 1 yuan. Now, a flower shop purchases between 1000 to 1500 roses and several lilies from Xiangyang Flower Base, and the shop spent exactly 9000 yuan on this purchase. Then, it sells the roses at 5 yuan and the lilies at 6.5 yuan each. The question is: How should the flower shop purchase these two types of flowers to maximize its gross profit?  
(Note: 1000 to 1500 plants means greater than or equal to 1000 plants and less than or equal to 1500 plants.  
Gross profit = Total amount received from selling lilies and roses - Total amount spent on purchasing lilies and roses)

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