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You are given a positive integer $M$. Find a positive integer $N$ and a sequence of non-negative integers $A = (A_1, A_2, \ldots, A_N)$ that satisfy all of the following conditions:

• $1 \le N \le 20$
• $0 \le A_i \le 10$ $(1 \le i \le N)$
• $\displaystyle \sum_{i=1}^N 3^{A_i} = M$

It can be proved that under the constraints, there always exists at least one such pair of $N$ and $A$ satisfying the conditions.

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$\displaystyle \sum_{i=1}^N 3^{A_i} = M$ 是啥意思？

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