eolymp
Competitions

XOR Contest

Cubes - 3

prb2807

Vitek has at home 2 identical sets of cubes of English letters, but during the regular cleaning one of the cubes was lost. Help Witek to determine which of the cubes is missing in one of the sets.

Input

The first line contains the number of found cubes n (1n105) by Vitek, and the second line contains n characters depicted on each of the cubes.

Output

Print the character on the lost cube, or the message "Ok", if Vitek was mistaken and no cube is lost.

Time limit 1 second
Memory limit 122.17 MiB
Input example #1
5
abcac
Output example #1
b
Author Anatoliy Prisyazhnuk
Source II этап Всеукраинской олимпиады школьников 2012-2013, г. Бердичев