A. Bracket Sequence
data structures; expression parsing; implementation
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 = s1s2... s|s| (where |s| is the length of string s) is the string slsl + 1... sr. 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.
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 105 characters.
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.