Problem F
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.
| Sample Input 1 | Sample Output 1 |
|---|---|
4 4 luka o#a# kula i#a# |
kala |
| Sample Input 2 | Sample Output 2 |
|---|---|
4 4 luka o#a# kula i#as |
as |
| Sample Input 3 | Sample Output 3 |
|---|---|
4 5 adaca da##b abb#b abbac |
abb |