
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
Let $f(x)=\left\{{\begin{array}{l}{{x^2},x＜0}\\{x+1,x≥0}\end{array}}\right.$. If $f\left(f\left(a\right)\right)=4$, then the real number $a$ is $\_\_\_\_\_\_$.

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