@SuppressWarnings("rawtypes")
	private static String select_login() {
		String result = null;
		System.out.print("available login: ");
		Map<String, UserManager.User> users = UserManager.getInstance().users();
		Iterator it = users.entrySet().iterator();
		int i = 0;
	    while (it.hasNext()) {
	        Map.Entry pairs = (Map.Entry)it.next();
	        System.out.print("[" + i++ + "]" + pairs.getKey() + "; ");
	    }
	    System.out.println();
	    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
	    String input = null;
	    try {
	    	input = reader.readLine();
	    }catch (IOException e) {
            e.printStackTrace();
        } 
	    int number;
	    try {
	    	number = Integer.parseInt(input);
	    } catch (Exception e) {
	    	ExceptionHandler.stringToInteger(input);
	    	return null;
	    }
	    if(number >= i || number < 0) {
	    	System.out.println("input number `" + number + "` is too big");
	    	result = null;
	    } else {
	    	i = 0;
	    	it = users.entrySet().iterator();
		    while (i < users.size()) {
		        Map.Entry pairs = (Map.Entry)it.next();
		        if(number == i++) {
		        	result = (String) pairs.getKey();
		        	break;
		        }
		    }
	    }
	    return result;
	}