В Idea отрабатывает нормально но валидатор не согласен!!!!

package com.javarush.task.task18.task1819;

/*
Объединение файлов
*/

import java.io.*;


public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader kb=new BufferedReader(new InputStreamReader(System.in));
        String fn1=kb.readLine();
        String fn2=kb.readLine();
        kb.close();

        byte[] buff;
/*
        File f1 = new File(fn1);
        File f2 = new File(fn2);
        int fl1 = (int) f1.length();
        int fl2 = (int) f2.length();
*/
        int fl2 = (int) new FileInputStream(fn2).getChannel().size();
        FileInputStream fr = new FileInputStream(fn1);
        int fl1 = (int) fr.getChannel().size();
        int iBuffSize=fl1 + fl2;
        buff = new byte[iBuffSize];
        fr.read(buff,fl2,fl1);
        fr.close();

        fr = new FileInputStream(fn2);
        fr.read(buff,0,fl2);
        fr.close();

        FileOutputStream fo = new FileOutputStream(fn1);
        fo.write(buff,0,iBuffSize);
        fo.close();
    }
}