CF1146A.Love "A"

Alice has a string $s$. She really likes the letter "a". She calls a string good if strictly more than half of the characters in that string are "a"s. For example "aaabb", "axaa" are good strings, and "baca", "awwwa", "" (empty string) are not.

Alice can erase some characters from her string $s$. She would like to know what is the longest string remaining after erasing some characters (possibly zero) to get a good string. It is guaranteed that the string has at least one "a" in it, so the answer always exists.

Alice 有一个字符串 $s$。她非常喜欢字母 “a”。如果一个字符串中 “a” 的个数严格大于该字符串长度的一半，则称这个字符串为好字符串。例如，“aaabb”、“axaa” 是好字符串，而 “baca”、“awwwa”、""（空字符串）则不是。

Alice 可以从她的字符串 $s$ 中删除一些字符（也可以不删）。她想知道：在删除若干字符（可能为零）后，能得到的最长的好字符串的长度是多少？题目保证字符串 $s$ 中至少包含一个 “a”，因此答案一定存在。

The first line contains a string $s$ ($1 \leq |s| \leq 50$) consisting of lowercase English letters. It is guaranteed that there is at least one "a" in $s$.

第一行包含一个字符串 $s$（$1 \leq |s| \leq 50$），由小写英文字母组成。保证 $s$ 中至少有一个字符 "a"。

Print a single integer, the length of the longest good string that Alice can get after erasing some characters from $s$.

输出一个整数，表示爱丽丝从字符串 $s$ 中删除若干字符后所能得到的最长“好字符串”的长度。

In the first example, it's enough to erase any four of the "x"s. The answer is $3$ since that is the maximum number of characters that can remain.

In the second example, we don't need to erase any characters.

在第一个例子中，只需删除任意四个“x”即可。答案为 $3$，因为这是可以保留的最多字符数量。

在第二个例子中，我们无需删除任何字符。