Java: save file into two different files - please explain me solution

I have a problem with one of the tasks:
Read 3 file names from console: file1, file2, file3.
Divide file:
Save half of bites into file2 and second half into file3.
If number of bytes is not even save more bytes into file2.
Close streams.

I was wondering how to solve it and the only solution that works properly is:

public class main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String a = reader.readLine();
        String b = reader.readLine();
        String c = reader.readLine();

        FileInputStream fileInputStream1 = new FileInputStream(a);
        FileOutputStream fileOutputStream2 = new FileOutputStream(b);
        FileOutputStream fileOutputStream3 = new FileOutputStream(c);

        byte[] buffer = new byte[fileInputStream1.available()];

        if (fileInputStream1.available() % 2 != 0) {
            while (fileInputStream1.available() > 0) {
                int count = fileInputStream1.read(buffer);
                fileOutputStream2.write(buffer, 0, count / 2+1);
                fileOutputStream3.write(buffer, count / 2+1, count/2);
            }
        } else {
            while (fileInputStream1.available() > 0) {
                int count = fileInputStream1.read(buffer);
                fileOutputStream2.write(buffer, 0, count / 2);
                fileOutputStream3.write(buffer, count / 2, count/2);
            }
        }

        fileInputStream1.close();
        fileOutputStream2.close();
        fileOutputStream3.close();
    }
}

My question is: why do I have to save from count/2 to count/2? It does not make any sense to me. If I will use numbers, let's assume that file1 has 100 bytes. I save from 0 to count/2 (100/2=50) and from count/2 to count/2 (from 100/2=50 to 100/2=50 or even 50/2=25).
In my opinion it should be from 0 to count/2 and from count/2 to count or buffer.length

Please explain me why my solutions are wrong comparing to correct one.
Thank you.

Here is the explanation.First program makes a buffer reader whose source is keyboard entry. Then program reads line by line and saves the results in appropriate strings. Then program makes streams for reading and writing in files (so called file streams). After that all of the bytes from input file are read and put in buffer byte array. First
we need to cheek if byte number in file is even or odd and then do the appropriate actions of copying bytes into arrays.
Have in mind when copying buffer array than range is exclusive at end and inclusive at start e.g. Arrays.copyOfRange(buffer, 0, buffer.length / 2) copies bytes in this interval [0,buffer.length / 2>. Now we only need to write the bytes in respective files. Hope this helps.

       public static void main(String[] args) throws IOException  {
  
       BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
	
        String inputFile = reader.readLine();
        String outFile2 = reader.readLine();
        String outFile3 = reader.readLine();
        
        FileInputStream  fileInputStream1  = new FileInputStream(inputFile);
		FileOutputStream fileOutputStream2 = new FileOutputStream(outFile2);
		FileOutputStream fileOutputStream3 = new FileOutputStream(outFile3);
         
		byte[] buffer = Files.readAllBytes(Paths.get(inputFile));
		byte[] bytesForOut2, bytesForOut3;
		
		if(buffer.length % 2 == 0) {
			bytesForOut2 = Arrays.copyOfRange(buffer, 0, buffer.length / 2);
			bytesForOut3 = Arrays.copyOfRange(buffer, buffer.length /2, buffer.length);
		}
		else {
			bytesForOut2 = Arrays.copyOfRange(buffer, 0, buffer.length / 2 + 1);
			bytesForOut3 = Arrays.copyOfRange(buffer, buffer.length /2 + 1, buffer.length);
		}
		
		fileOutputStream2.write(bytesForOut2);
		fileOutputStream3.write(bytesForOut3);
		
		fileInputStream1.close();
		fileOutputStream2.close();
		fileOutputStream3.close();

}