
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
If a four-digit natural number $t$ has no digit equal to $0$ and satisfies that the sum of the thousands digit and the tens digit is $9$, and the difference between the hundreds digit and the units digit is $1$, then $t$ is called a "nine-one number". Let the sum of the two times the thousands digit of $t$ and the units digit be denoted as $P(t)$, and the sum of the two times the hundreds digit and the tens digit be denoted as $Q(t)$. Define $G(t) = \frac{{2P(t)}}{{Q(t)}}$. When $G(t)$ is an integer, $t$ is called a "whole nine-one number". If $M = 2000a + 100b + 10c + d$ (where $1 \leq a \leq 4$, $1 \leq b \leq 9$, $1 \leq c \leq 9$, $1 \leq d \leq 9$ and $a$, $b$, $c$, $d$ are all integers) is a "whole nine-one number", then the maximum value of $M$ that satisfies the conditions is ______.

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