P8392 [BalticOI 2022] Uplifting Excursion (Day1)

There are $2m+1$ types of items, with weights $-m,-m+1,\ldots, m-1,m$. There are $a_i$ items of weight $i$. You need to take some items such that the sum of their weights is exactly $l$. Under this condition, you need to take as many items as possible. Ask: with the total weight exactly $l$, what is the maximum number of items you can take.

The first line contains two numbers $m,l$. The second line contains $2m+1$ numbers: $a_{-m},a_{-m+1},\ldots, a_{m-1},a_m$.

Output one number in a single line, representing the answer. If no solution exists, output `impossible`.

Subtask $1$ ($5$ points): $m , a_i≤50$. Subtask $2$ ($15$ points): $m , a_i≤100$. Subtask $3$ ($20$ points): $m≤30$. Subtask $4$ ($20$ points): $m ≤50$. Subtask $5$ ($20$ points): $m ≤ 100$. Subtask $6$ ($20$ points): no special constraints. For subtasks $3$ to $6$, if you pass the test points with $\forall i