Lexicographic Order

题号：NC232091
时间限制：C/C++/Rust/Pascal 1秒，其他语言2秒
空间限制：C/C++/Rust/Pascal 256 M，其他语言512 M
64bit IO Format: %lld

题目描述

Nana7mi has a string $s$ with length of $n$ and containing only lowercase characters.
Now she wants to know the lexicographically greatest string $t$ with length not exceed $m$ , containing only lowercase characters and is lexicographically less than $s$ .

String $x$ is lexicographically less than string $y$ , if either $x$ is a prefix of $y$ (and $x \neq y$ ), or there exists such $i (1 \le i \le min(|x|,|y|)$ ), that $x_i < y_i$ , and for any $j (1 \le j < i) x_j = y_j$ . Here $|a|$ denotes the length of the string $a$ .

输入描述:

The first line of input contains two integers  --- the length of  and the length limit of .
The second line contains a string  with length of , as the string Nana7mi has.

输出描述:

Output a string with length not exceed  and containing only lowercase characters in a line.

示例1

输入

复制

3 4
ybb

输出

复制

ybaz