import java.util.ArrayList;

import java.util.List;

public class Atbash {

private static final int GROUP_SIZE = 5;

private static final String PLAIN = "abcdefghijklmnopqrstuvwxyz";

private static final String CIPHER = "zyxwvutsrqponmlkjihgfedcba";

public static String encode(String input) {

String encoded = stripInvalidCharacters(input).toLowerCase();

String cyphered = "";

for (char c : encoded.toCharArray()) {

cyphered += applyCipher(c);

}

return splitIntoFiveLetterWords(cyphered);

}

public static String decode(String input) {

String encoded = stripInvalidCharacters(input).toLowerCase();

String deciphered = "";

for (char c : encoded.toCharArray()) {

deciphered += applyCipher(c);

}

return deciphered;

}

private static String stripInvalidCharacters(String input) {

String filteredValue = "";

for (char c : input.toCharArray()) {

if (Character.isLetterOrDigit(c)) {

filteredValue += c;

}

}

return filteredValue;

}

private static char applyCipher(char input) {

int idx = PLAIN.indexOf(input);

return idx >= 0 ? CIPHER.toCharArray()[idx] : input;

}

private static String splitIntoFiveLetterWords(String value) {

List<String> words = new ArrayList<>();

for (int i = 0; i < value.length(); i += GROUP_SIZE) {

words.add(i + GROUP_SIZE <= value.length() ? value.substring(i, i + GROUP_SIZE) : value.substring(i));

}

return String.join(" ", words);

}

}