Package for this problem was not updated by the problem writer or Codeforces administration after we’ve upgraded the judging servers. To adjust the time limit constraint, solution execution time will be multiplied by 2. For example, if your solution works for 400 ms on judging servers, then value 800 ms will be displayed and used to determine the verdict.

Virtual contest is a way to take part in past contest, as close as possible to participation on time. It is supported only ACM-ICPC mode for virtual contests.
If you've seen these problems, a virtual contest is not for you - solve these problems in the archive.
If you just want to solve some problem from a contest, a virtual contest is not for you - solve this problem in the archive.
Never use someone else's code, read the tutorials or communicate with other person during a virtual contest.

No tag edit access

B. New Problem

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputComing up with a new problem isn't as easy as many people think. Sometimes it is hard enough to name it. We'll consider a title original if it doesn't occur as a substring in any titles of recent Codeforces problems.

You've got the titles of *n* last problems — the strings, consisting of lowercase English letters. Your task is to find the shortest original title for the new problem. If there are multiple such titles, choose the lexicographically minimum one. Note, that title of the problem can't be an empty string.

A substring *s*[*l*... *r*] (1 ≤ *l* ≤ *r* ≤ |*s*|) of string *s* = *s*_{1}*s*_{2}... *s*_{|s|} (where |*s*| is the length of string *s*) is string *s*_{l}*s*_{l + 1}... *s*_{r}.

String *x* = *x*_{1}*x*_{2}... *x*_{p} is lexicographically smaller than string *y* = *y*_{1}*y*_{2}... *y*_{q}, if either *p* < *q* and *x*_{1} = *y*_{1}, *x*_{2} = *y*_{2}, ... , *x*_{p} = *y*_{p}, or there exists such number *r* (*r* < *p*, *r* < *q*), that *x*_{1} = *y*_{1}, *x*_{2} = *y*_{2}, ... , *x*_{r} = *y*_{r} and *x*_{r + 1} < *y*_{r + 1}. The string characters are compared by their ASCII codes.

Input

The first line contains integer *n* (1 ≤ *n* ≤ 30) — the number of titles you've got to consider. Then follow *n* problem titles, one per line. Each title only consists of lowercase English letters (specifically, it doesn't contain any spaces) and has the length from 1 to 20, inclusive.

Output

Print a string, consisting of lowercase English letters — the lexicographically minimum shortest original title.

Examples

Input

5

threehorses

goodsubstrings

secret

primematrix

beautifulyear

Output

j

Input

4

aa

bdefghijklmn

opqrstuvwxyz

c

Output

ab

Note

In the first sample the first 9 letters of the English alphabet (a, b, c, d, e, f, g, h, i) occur in the problem titles, so the answer is letter j.

In the second sample the titles contain 26 English letters, so the shortest original title cannot have length 1. Title aa occurs as a substring in the first title.

Codeforces (c) Copyright 2010-2019 Mike Mirzayanov

The only programming contests Web 2.0 platform

Server time: Mar/25/2019 07:47:32 (d1).

Desktop version, switch to mobile version.

Supported by

User lists

Name |
---|