import java.io.*;

public class CopyLines {
  public static void main(String[] args) throws IOException {
    
    String filename;
    if(args.length > 0)
      filename = args[0];
    else
      filename = "xanadu.txt";

    try (BufferedReader reader = new BufferedReader(new FileReader(filename));
         PrintWriter writer = new PrintWriter(new FileWriter("__"+filename))
        ) {

      String line;
      while ((line = reader.readLine()) != null) {
        writer.println(line);
      }
    } 
  }
}