public class Parseint {
    public static int parseInt(String str) {
        if (str == null || str.isEmpty()) {
            System.out.println("Der String enthaelt keine Zeichen");
            return -1;
        } else {
            int sum = 0;
            int position = 1;
            for (int i = str.length() - 1; i >= 0; i--) {
                int number = str.charAt(i) - '0';
                sum += number * position;
                position = position * 10;

            }
            return sum;
        }
    }

    public static void main(String[] args) {
        int a = parseInt("");
        System.out.println(a);

    }
}