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.

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.

Constraints

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

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.

见题面 Input 部分

见题面 Output 部分