public static String everyNth(String s, int n)
    {
        if (n < 0) {
            throw new IllegalArgumentException();
        }else if (s.length() > n){
            String newS = s.substring(n,s.length());
            return s.charAt(n-1) + everyNth(newS, n);
        } else {
            return s.substring(0,s.length()-(s.length()%n));
        }
    }

    public static String noNth(String s, int n)
    {
        if (n < 0) {
            throw new IllegalArgumentException();
        }else if (s.length() > n){
            String newS = s.substring(n,s.length());
            return s.substring(0, n-1) + noNth(newS, n);
        } else {
            return s;
        }
    }