Bracket Sequence

题意翻译

## 题目描述： 对于一个括号序列，只含有```(```、```)```、```[```、```]```这四种括号。一个括号序列是合法的，当且仅当能在里面加上若干个```1```和```+```，使其成为一个正确的表达式（其中两种括号均可以互相嵌套）。给定一个括号序列，请找到它的一个子串，使得它是合法的，且其中```[```最多。 ## 输出格式： 第一行一个数，表示```[```最多的次数；\ 第二行输出此时的子串。

题目描述

A bracket sequence is a string, containing only characters "(", ")", "\[" and "\]". A correct bracket sequence is a bracket sequence that can be transformed into a correct arithmetic expression by inserting characters "1" and "+" between the original characters of the sequence. For example, bracket sequences "()\[\]", "(\[\])" are correct (the resulting expressions are: "(1)+\[1\]", "(\[1+1\]+1)"), and "\](" and "\[" are not. The empty string is a correct bracket sequence by definition. A substring $ s[l...\ r] $ $ (1<=l<=r<=|s|) $ of string $ s=s_{1}s_{2}...\ s_{|s|} $ (where $ |s| $ is the length of string $ s $ ) is the string $ s_{l}s_{l+1}...\ s_{r} $ . The empty string is a substring of any string by definition. You are given a bracket sequence, not necessarily correct. Find its substring which is a correct bracket sequence and contains as many opening square brackets «\[» as possible.

输入输出格式

输入格式

The first and the only line contains the bracket sequence as a string, consisting only of characters "(", ")", "\[" and "\]". It is guaranteed that the string is non-empty and its length doesn't exceed $ 10^{5} $ characters.

输出格式

In the first line print a single integer — the number of brackets «\[» in the required bracket sequence. In the second line print the optimal sequence. If there are more than one optimal solutions print any of them.

输入输出样例

输入样例 #1

([])

输出样例 #1

1
([])

输入样例 #2

(((

输出样例 #2

0