
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
Given the following four problems:  
① Input a number $x$, output its absolute value; ② Find the perimeter of a square with an area of 6; ③ Find the maximum number among three numbers $a$, $b$, and $c$; ④ Calculate the function value of $f(x)$.  
Among these, the number of problems that require a selection structure to describe the algorithm is $\_\_\_\_\_\_\_\_$.

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