Longest Unbalanced Subsequence

You are given a String consists of only '[', ']', '(', ')', '{', '}' these characters.
You need to find out the length of the longest subsequence which is unbalanced.

Note that:

A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.

A String is balanced if

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.