
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 communication company has launched a series of mobile phone card numbers, with the first seven digits fixed, ranging from "×××××××0000" to "×××××××9999", totaling 10,000 numbers. The company stipulates that any card number with the last four digits containing the number "4" or "7" will be considered as a "discount card". Determine the number of "discount cards" in this series.

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