False Sense of Security Solution:

import java.util.*;

public class Kattis {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String originalLine;
    HashMap<Character, String> hm = new HashMap<>();
    hm.put('A', "12");
    hm.put('B', "2111");
    hm.put('C', "2121");
    hm.put('D', "211");
    hm.put('E', "1");
    hm.put('F', "1121");
    hm.put('G', "221");
    hm.put('H', "1111");
    hm.put('I', "11");
    hm.put('J', "1222");
    hm.put('K', "212");
    hm.put('L', "1211");
    hm.put('M', "22");
    hm.put('N', "21");
    hm.put('O', "222");
    hm.put('P', "1221");
    hm.put('Q', "2212");
    hm.put('R', "121");
    hm.put('S', "111");
    hm.put('T', "2");
    hm.put('U', "112");
    hm.put('V', "1112");
    hm.put('W', "122");
    hm.put('X', "2112");
    hm.put('Y', "2122");
    hm.put('Z', "2211");
    hm.put('_', "1122");
    hm.put('.', "2221");
    hm.put(',', "1212");
    hm.put('?', "2222");
    HashMap<String, Character> reverse_hm = new HashMap<>();
    reverse_hm.put("12"  ,'A');
    reverse_hm.put("2111",'B');
    reverse_hm.put("2121",'C');
    reverse_hm.put("211" ,'D');
    reverse_hm.put("1"   ,'E');
    reverse_hm.put("1121",'F');
    reverse_hm.put("221" ,'G');
    reverse_hm.put("1111",'H');
    reverse_hm.put("11"  ,'I');
    reverse_hm.put("1222",'J');
    reverse_hm.put("212" ,'K');
    reverse_hm.put("1211",'L');
    reverse_hm.put("22"  ,'M');
    reverse_hm.put("21"  ,'N');
    reverse_hm.put("222" ,'O');
    reverse_hm.put("1221",'P');
    reverse_hm.put("2212",'Q');
    reverse_hm.put("121" ,'R');
    reverse_hm.put("111" ,'S');
    reverse_hm.put("2"   ,'T');
    reverse_hm.put("112" ,'U');
    reverse_hm.put("1112",'V');
    reverse_hm.put("122" ,'W');
    reverse_hm.put("2112",'X');
    reverse_hm.put("2122",'Y');
    reverse_hm.put("2211",'Z');
    reverse_hm.put("1122",'_');
    reverse_hm.put("2221",'.');
    reverse_hm.put("1212",',');
    reverse_hm.put("2222",'?');
    while (sc.hasNextLine()) {
      originalLine = sc.nextLine();
      StringBuilder sb = new StringBuilder();
      StringBuilder sb2 = new StringBuilder();
      StringBuilder result = new StringBuilder();
      for (int i = 0; i < originalLine.length(); i++) {
        sb.append(hm.get(originalLine.charAt(i)));
        sb2.append(hm.get(originalLine.charAt(i)).length());
      }
      String numbers = sb2.reverse().toString();
      int numcount = 0;
      for (int i = 0; i < originalLine.length(); i++) {
        result.append(reverse_hm.get(sb.substring(numcount, numcount + Character.digit(numbers.charAt(i), 10))));
        numcount += Character.digit(numbers.charAt(i), 10);
      }
      System.out.println(result);
    }
  }
}