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Score : $100$ points

### Problem Statement

You are given a string $S$ of length $3$.
Print a character that occurs only once in $S$.
If there is no such character, print -1 instead.

### Constraints

• $S$ is a string of length $3$ consisting of lowercase English letters.

### Input

Input is given from Standard Input in the following format:

$S$


### Output

Print the answer. If multiple solutions exist, you may print any of them.

### Sample Input 1

pop


### Sample Output 1

o


o occurs only once in pop.

### Sample Input 2

abc


### Sample Output 2

a


a, b, and c occur once each in abc, so you may print any of them.

### Sample Input 3

xxx


### Sample Output 3

-1


No character occurs only once in xxx.