Problem C
Prva

Little Ivica solves crossword puzzles every day. In case you haven’t seen one, a crossword puzzle starts on a grid of $R\times C$ squares, each of which is either empty or blocked. The player’s task is to write words in consecutive empty squares vertically (top down) or horizontally (left to right).

Ivica’s sister has a strange habit of looking at crosswords Ivica has finished solving, and finding the lexicographically smallest word in it. She only considers words at least $2$ characters long.

Write a program that, given a crossword puzzle, finds that word.

Input

The first line contains two integers $R$ and $C$ ($2\le R,C\le 20$), the number of rows and columns in the crosswords.

Each of the following $R$ lines contains a string of $C$ characters. Each of those characters is either a lowercase letter of the English alphabet, or the character ‘#’ representing a blocked square.

The input will be such that a solution will always exist.

Output

Output the lexicographically smallest word in the crossword.

4 4
luka
o#a#
kula
i#a#

kala

4 4
luka
o#a#
kula
i#as

as

4 5
adaca
da##b
abb#b
abbac

abb