Что теперь не так?)
package com.javarush.task.task18.task1808;
/*
Разделение файла
*/
import java.io.*;
import java.util.Arrays;
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String fileName1 = reader.readLine();
String fileName2 = reader.readLine();
String fileName3 = reader.readLine();
FileInputStream fileInputStream = new FileInputStream(fileName1);
FileOutputStream fileOutputStream1 = new FileOutputStream(fileName2);
FileOutputStream fileOutputStream2 = new FileOutputStream(fileName3);
byte[] buffer = new byte[fileInputStream.available()];
int size = 0;
while (fileInputStream.available() > 0) {
size = fileInputStream.read(buffer);
}
fileOutputStream1.write(buffer, 0, size / 2 + size % (size / 2));
fileOutputStream2.write(buffer, size / 2 + size % (size / 2), size / 2);
fileInputStream.close();
fileOutputStream1.close();
fileOutputStream2.close();
}
}