시간 제한메모리 제한제출정답맞은 사람정답 비율
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## 문제

A word $w$ is called bordered if there exists a word $u$, other then $w$ and empty word $\varepsilon$, such that $u$ is both suffix and prefix if $w$. For example, a word <<abbababb>> is bordered because <<abb>> is both its prefix and its suffix. A word that is not bordered is called borderless. For example, a word <<aabab>> is borderless.

Consider all borderless words of length $n$ composed of letters <<a>> and <<b>>. Let us denote the number of such words as $C_n$. Order them lexicographically --- by the first letter, then by the second one, etc, and number from 1 to $C_n$. Given $k$ find the $k$-th word in this order.

## 입력

The input file contains multiple test cases.

Each test case contains two integers $n$ and $k$ on a line ($1 \le n \le 64$, $1 \le k \le C_n$).

Input is followed by a line with $n = k = 0$. There are at most 1000 test cases in one input file.

## 출력

For each test case output one line --- the $k$-th lexicographically borderless word of length $n$.

## 예제 입력 1

5 1
5 2
5 3
5 4
5 5
0 0


## 예제 출력 1

aaaab
aaabb
aabab
aabbb
ababb