프로그램 명: coci_trener
제한시간: 1 초

[문제요약] 성(surname) 의 첫글자가 같은 사람의 수가 5 명 이상인 첫 글자를 알파벳순으로 출력하는 문제.

존재하지 않는다면 PREDAJA 를 출력

Mirko has been moving up in the world of basketball, starting as a mere spectator, mastering snack salesmanship, finally reach the coveted position of the national team coach. He is now facing a difficult task: selecting the five primary players for the upcoming match against Tajikistan.

Since Mirko is incredibly lazy, he doesn't bother remembering players' names, let alone their actual skills. That's why he has settled on selecting five players who share the same first letter of their surnames, so that he can remember them more easily. If there are no five players sharing the first letter of their surnames, Mirko will simply forfeit the game!

In order to obtain insight into possibilities for his team, Mirko wants to know all the different letters that his primary team's surnames may begin with.

입력

The first line of input contains the positive integer N (1 ≤ N ≤ 150), the number of players that Mirko has available.

Each of the following N lines contains one word (at most 30 characters long, consisting only of lowercase English letters), a surname of one of the players.

출력

If there are no five players that Mirko can select matching his criteria, output a single line containing the word “PREDAJA” (without quotes). Otherwise, output all possible first letters of representation player surnames, sorted lexicographically, in a single line with no spaces.

입출력 예

input 

18 
babic 
keksic 
boric 
bukic 
sarmic 
balic 
kruzic 
hrenovkic 
beslic 
boksic 
krafnic 
pecivic 
klavirkovic 
kukumaric 
sunkic 
kolacic 
kovacic 
prijestolonasljednikovic 

output 

bk 

input 

6 
michael 
jordan 
lebron 
james 
kobe 
bryant 

output 

PREDAJA 

출처:coci/2013-2014/contest1
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