[USACO12FEB] Cow IDs S

Being a secret computer geek, Farmer John labels all of his cows with binary numbers. However, he is a bit superstitious, and only labels cows with binary numbers that have exactly K "1" bits $(1 \le K \le 10)$. The leading bit of each label is always a "1" bit, of course. FJ assigns labels in increasing numeric order, starting from the smallest possible valid label -- a K-bit number consisting of all "1" bits. Unfortunately, he loses track of his labeling and needs your help: please determine the Nth label he should assign $(1 \le N \le 10^7)$. FJ 给他的奶牛用二进制进行编号，每个编号恰好包含 $K$ 个 $1$（$1 \le K \le 10$），且必须是 $1$ 开头。FJ 按升序编号，第一个编号是由 $K$ 个 $1$ 组成。 请问第 $N$（$1 \le N \le 10^7$）个编号是什么。

* Line $1$: Two space-separated integers, $N$ and $K$.

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