public String factor(int x) {
      String line="";
      try {
         Runtime rt=Runtime.getRuntime();
         Process pr=rt.exec("factor "+x);
         java.io.BufferedReader reader=new java.io.BufferedReader(new java.io.InputStreamReader(pr.getInputStream()));
         line=reader.readLine();
         System.out.println(line);
      } catch(Exception e) {
         e.printStackTrace();
         System.exit(-1);
      }
      return line;
   }