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