import plp.collection.SList;

class TestSList {
    public static void main(String[] args) {
	SList sl = SList.EMPTY;
	for (int i = 0; i < args.length; ++i) {
	    sl = new SList(args[i], sl);
	}
	sl = sl.reverse().append(sl);
	System.out.println(sl);
    }
}