Alice is traveling to a special town with her friends. All the residents of this special town communicate through a special language. This special language consists of special alphabets and . This language contains special words. These words are composed of these special alphabets and are always even in length. The words are always palindromic in nature. The words are also assigned special numbers. A special number is the lexicographical rank of special word with respect to other special words.
You are given a special number. Your task is to determine the special word corresponding to that special number.
Note: A palindrome sequence that reads the same backward as forwards. For example, , , and so on.
Input format
Output format
For each test case, print a string that denotes the special number corresponding to the special number in a new line.
Constraints
The first special words are .