
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
Read the pseudocode shown in the diagram. If the algorithm is executed to calculate the result of $-1 + 3 - 5 + 7 - 9$, then the initial value of $a$, $x = \boxed{\_\_\_\_\_\_\_\_}$.

```
S←0  
a←x  
For I From 1 To 9 Step 2  
S←S + a×I  
a←a×(-1)  
End For  
Print S
```

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