public static String conc(int max) {
        String s = "a";
        String ret = "a";
        for (int i = 0; i < max; i++) {
            ret += "a";
        }
        return ret;
    }

    public static String sb(int max) {
        String s = "a";
        StringBuilder ret = new StringBuilder(s);
        for (int i = 0; i < max; i++) {
            ret.append("a");
        }
        return ret.toString();
    }