
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
In triangle $ABC$, $\overrightarrow{AD} = 4\overrightarrow{DC}$, $E$ is the midpoint of $AB$, let $\overrightarrow{AB} = \overrightarrow{a}$, $\overrightarrow{BC} = \overrightarrow{b}$. If $\overrightarrow{DE} = \lambda_1 \overrightarrow{a} + \lambda_2 \overrightarrow{b}$, then $\lambda_1 + \lambda_2 = \_\_\_\_\_\_$.

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