P12454 [INOI Team Selection 2021] String

Mikaeel has got $n$ strings named $s_{1}, \ldots, s_{n}$ each consists of lower-case English letters. He wants to pick a non-empty substring of each one and concatenate them together to make a final string of size $k$. Help Mikaeel create the smallest lexicographical string possible.

In the first line, you are given two integers $n$ and $k$, the number of strings and the size of the final string, respectively. The $n$ following lines contain the sequence $s_{1}, \ldots, s_{n}$, the strings of Mikaeel.

In a single line, print the smallest lexicographical string achievable.

### Constraints - $n, \sum_{i=1}^{n}\left|s_{i}\right| \leq 4000$ - $n \leq k \leq \sum_{i=1}^{n}\left|s_{i}\right|$ ### Subtasks | subtask | score | limits | | :---: | :---: | :---: | | 1 | 23 | $\forall_{1 \leq i \leq n}, \vert s_{i}\vert = \vert s_{1}\vert \leq 10$，$1 \leq n \leq 50$ | | 2 | 19 | $\forall_{1 \leq i \leq n}, \vert s_{i}\vert = \vert s_{1} \vert \leq 20$, $1 \leq n \leq 200$ | | 3 | 58 | No extra limits |