DRM Messages Solution:

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Kattis {
    public static void main(String[] args) {
        String line = new Scanner(System.in).nextLine();
        StringBuilder sb = new StringBuilder();
        String[] firstPart = line.substring(0, line.length() /2).split("");
        String[] secondPart = line.substring(line.length() /2, line.length()).split("");
        int firstRotate =  Arrays.stream(firstPart).mapToInt(i -> i.charAt(0) - 'A').sum();
        int secondRotate = Arrays.stream(secondPart).mapToInt(i -> i.charAt(0) - 'A').sum();
        Arrays.stream(firstPart).map((String s) -> rotate(s.charAt(0), firstRotate)).collect(Collectors.toList()).toArray(firstPart);
        Arrays.stream(secondPart).map((String s) -> rotate(s.charAt(0), secondRotate)).collect(Collectors.toList()).toArray(secondPart);
        IntStream.range(0, firstPart.length).forEach(i -> sb.append(rotate(firstPart[i].charAt(0), secondPart[i].charAt(0) - 'A')));
        System.out.println(sb);
    }
    static String rotate(char e, int rotate){
        return Character.toString((char)((e - 'A' + rotate) % 26 + 'A'));
    }
}