Iteration of String (Letters and Numbers) to collect in hash

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class TestIXIII {
    public static void test1() {
        String input = "1122\n" +
                "A1B12C11D2";
        System.setIn(new ByteArrayInputStream(input.getBytes()));
    }

    public static void main(String[] args) throws IOException {
        test1();
        //  BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        Scanner scanner = new Scanner(System.in);
        String secretCode = scanner.nextLine();
        String cipher = scanner.nextLine();
        TreeMap<Integer, Character> myMap = new TreeMap<>();
        Stack<Character> letters = new Stack<>();

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

            if (Character.isDigit(cipher.charAt(i))) {
                String valueStr = "" + cipher.charAt(i);
                while (true) {
                    i++;
                    if (i < cipher.length() && Character.isDigit(cipher.charAt(i))) {
                        valueStr += cipher.charAt(i);
                    } else {
                        i--;
                        break;
                    }
                }

                int key = Integer.parseInt(valueStr);
                char value = letters.pop();
                myMap.put(key, value);

            } else {
                letters.add(cipher.charAt(i));
            }
        }

        System.out.println(myMap.get(111));
    }
}