Deciphering

package finalExamPrep;

import java.util.Map;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Deciphering {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        String input=scanner.nextLine();

        String regex="^([d-z,|#]+)$";
        Pattern pattern=Pattern.compile(regex);
        Matcher matcher = pattern.matcher(input);
        String[]substrings=scanner.nextLine().split(" ");
        StringBuilder builder= new StringBuilder();
        StringBuilder builder2=new StringBuilder();

        if (matcher.find()){
            for (int i = 0; i <input.length() ; i++) {
                int num=input.charAt(i)-3;
                builder.append((char)num);
            }
            input=builder.toString();
            input=input.replace(substrings[0],substrings[1]);
            System.out.println(input);
        }else {
            System.out.println("This is not the book you are looking for.");
        }

    }
}