{"raw_statement":[{"iden":"problem statement","content":"We have $N$ cards. The $i$\\-th card has a string $S_i$ written on it.\nFind the lexicographically smallest string that can be obtained by choosing $K$ of these cards and concatenating them in any order."},{"iden":"constraints","content":"*   $1 \\leq K \\leq N \\leq 50$\n*   $1 \\leq |S_i| \\leq 50$\n*   $S_i$ consists of lowercase English letters."},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$N$ $K$\n$S_1$\n$S_2$\n$\\vdots$\n$S_N$"},{"iden":"sample input 1","content":"4 3\node\nzaaa\nr\natc"},{"iden":"sample output 1","content":"atcoder\n\nNote that it is not possible to reverse or permute the string written on a card.  \nFor example, `ode` written on the first card cannot be used as `edo` or `deo`."},{"iden":"sample input 2","content":"5 2\nz\nz\nzzz\nz\nzzzzzz"},{"iden":"sample output 2","content":"zz\n\nThere may be a pair $i, j$ $(i\\neq j)$ such that $S_i = S_j$."}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}