
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 plane vectors $\overrightarrow {OA}$, $\overrightarrow {OB}$, $\overrightarrow {OC}$ satisfy: $|\overrightarrow {OA}|=|\overrightarrow {OB}|=|\overrightarrow {OC}|=1$, $\overrightarrow {OA} \cdot \overrightarrow {OB}=0$. If $\overrightarrow {OC}=x \overrightarrow {OA}+y \overrightarrow {OB}$, ($x,y\in\mathbb{R}$), determine the maximum value of $x+y$.

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