Minimize the string

You are given **n** strings **s1, s2, ..., sn**. Each of these strings consists only of letters 'a' and 'b', and the length of each string can be at most 2. In other words, the only allowed strings are "a", "b", "aa", "ab", "ba" and "bb". Consider a permutation **p** = {**p1**, **p2**, ..., **pn**} of the integers {1, 2, ..., **n**}. Using this permutation, you can obtain a new string **S = sp1 +