import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class CopyCharacters {
  public static void main(String[] args) throws IOException {

    String filename;
    if(args.length > 0)
      filename = args[0];
    else
      filename = "xanadu.txt";
    
    try(FileReader reader = new FileReader(filename);
        FileWriter writer = new FileWriter("__"+filename)
       ) {
      int c;
      while ((c = reader.read()) != -1) {
        writer.write(c);
      }
    } 
  }
}