Не проходит валидацию.

public class Solution{

    public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        ByteArrayOutputStream byteArrayOutStream = new ByteArrayOutputStream();
        SortedSet<String> filesSet = new TreeSet<>();
        String lastWord = null;
        String fileNameFinal = null;
        while (true){
            lastWord = br.readLine();
            if(lastWord.equals("end")){break;}
            fileNameFinal = lastWord;
            filesSet.add(lastWord);
        }
        br.close();

        Iterator iter = filesSet.iterator();



        while (iter.hasNext()){

            FileInputStream fis = new FileInputStream(iter.next().toString());
            while (fis.available() > 0){
                byteArrayOutStream.write(fis.read());
            }
            fis.close();
        }

        fileNameFinal = fileNameFinal.substring(0, fileNameFinal.lastIndexOf("."));

        FileOutputStream fileAll = new FileOutputStream(fileNameFinal);
        byteArrayOutStream.writeTo(fileAll);



        byteArrayOutStream.close();
        fileAll.close();
    }
}