Problems
Only one letter
Only one letter
Print only small Latin letters $a$ found in the given string.
\InputFile
One line consisting only of small Latin letters and spaces.
\OutputFile
Print only small Latin letters $a$ from the given string. If the letter $a$ is not in the string, then print $-1$.
Input example #1
abrakadabra
Output example #1
aaaaa
Input example #2
qwertyuiop sdfghjkl
Output example #2
-1