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 $1$.)

The input is given from Standard Input in the following format: >$S$ #### Constraints - $S$ is a string of length between $1$ and $100$ (inclusive) consisting of lowercase English letters.

Print the answer.

***For Sample #1:*** `a` appears three times in $S$. The last occurrence is at index $7$, so you should print $7$. ***For Sample #2:*** `a` does not appear in $S$, so you should print $-1$.

AtCoder [ABC276A]