Score : $100$ points

问题描述

你将得到一个仅包含小写英文字母的字符串 $S$。

如果 a 在 $S$ 中出现，输出它最后一次出现的索引；否则，输出 $-1$。（索引从 $1$ 开始计数。）

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

You are given a string $S$ consisting of lowercase English letters. If a appears in $S$, print the last index at which it appears; otherwise, print $-1$. (The index starts at $1$.)

Constraints

• $S$ is a string of length between $1$ and $100$ (inclusive) consisting of lowercase English letters.

Input

The input is given from Standard Input in the following format:

$S$

Output

Print the answer.

Sample Input 1

abcdaxayz

Sample Output 1

7

a appears three times in $S$. The last occurrence is at index $7$, so you should print $7$.

Sample Input 2

bcbbbz

Sample Output 2

-1

a does not appear in $S$, so you should print $-1$.

Sample Input 3

aaaaa

Sample Output 3

5

update @ 2024/3/10 11:36:23