Pls help me figure out the bug
package com.codegym.task.task18.task1825;
import java.io.*;
import java.util.ArrayList;
/*
Building a file
*/
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
ArrayList<String> files = new ArrayList<>();
while (true) {
String filename = reader.readLine();
if (filename.equals("end")) break;
files.add(filename);
}
reader.close();
String fileName = files.get(0);
fileName = fileName.split(".part")[0];
File file = new File(fileName);
if(file.createNewFile()) {
file.setWritable(true);
FileOutputStream outputStream = new FileOutputStream(fileName);
for(int i = 1; i <= files.size(); i++) {
int index = files.indexOf(fileName+".part"+i);
FileInputStream inputStream = new FileInputStream(files.get(index));
while (inputStream.available() > 0) {
byte[] buffer = new byte[1000];
int count = inputStream.available();
inputStream.read(buffer);
if (count < 1000) {
outputStream.write(buffer, 0, count);
}
else {
outputStream.write(buffer);
}
}
inputStream.close();
}
outputStream.close();
}
}
}