public void part4() {
        //TextIO txtIO = new TextIO();        //inicializace objektu
        TextIO txtIO = new TextIO("input.txt");

        int count = 0;
        double sum = 0.0;
        boolean end = false;
        while (!end) {
            String line = txtIO.in.nextLine();
            if (line.length() > 0 && txtIO.isDouble(line)) {
                sum += Double.parseDouble(line);
                count++;
            } else {
                System.err.println("End of input detected!");
                end = true;
            }
        }
        while (!end) {

        }
        System.out.println("Sum of the " + count + " input numbers is " + sum);
    }