How to account for the header bmp in my program?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace A
{
    class Program
    {
        static int flush(FileStream output, byte currentX, int counter)
        {
            if (counter > 1)
            {
                output.WriteByte(currentX);
                output.WriteByte((byte)counter);
            }
            return 1;
        }

        static public void compress(String source, String dis)
        {
            FileStream input = new FileStream(source, FileMode.Open, FileAccess.Read);
            FileStream output = new FileStream(dis, FileMode.Create, FileAccess.Write);

            byte currentX = (byte)input.ReadByte();
            output.WriteByte(currentX);
            int counter = 1;

            while (input.Position != input.Length)
            {
                byte nextX = (byte)input.ReadByte();
                if (nextX == currentX)
                {
                    if (counter++ > 250)
                    {
                        counter = flush(output, currentX, counter);
                        currentX = (byte)input.ReadByte();
                        output.WriteByte(currentX);
                    }
                    continue;
                }

                counter = flush(output, currentX, counter);
                output.WriteByte(nextX);
                currentX = nextX;
                counter = 1;
            }
            counter = flush(output, currentX, counter);
            input.Close();
            output.Close();
        }

        static public void decompress(String source, String dis)
        {
            FileStream input = new FileStream(source, FileMode.Open, FileAccess.Read);
            FileStream output = new FileStream(dis, FileMode.Create, FileAccess.Write);

            byte currentX = (byte)input.ReadByte();
            output.WriteByte(currentX);

            while (input.Position < input.Length)
            {
                byte nextX = (byte)input.ReadByte();
                if (nextX == currentX)
                {
                    byte cnt = (byte)input.ReadByte();
                    for (int i = 2; i <= cnt; i++) output.WriteByte(currentX);
                    currentX = (byte)input.ReadByte();
                    output.WriteByte(currentX);
                }
                else
                {
                    output.WriteByte(nextX);
                    currentX = nextX;
                }
            }
        }

        static void Main(string[] args)
        {
            compress("input.bmp", "compressed.rle");
            decompress("compressed.rle", "inputO.bmp");
        }
    }
}