public class Main
{
    static String reverse(String s) {
        if(s.length()==0)
            return "";
        return s.charAt(s.length()-1) + reverse(s.substring(0, s.length()-1));
    }
    static void onetoN(int i,int n) {
        if(i>n)
            return;
        System.out.print(i+" ");
        onetoN(i+1,n);
    }
    static int sum(int n) {
        if(n==0){
            return 0;
        }
        return n+sum(n-1);
    }
	public static void main(String[] args) {
		System.out.println("Hello World");
		String v=reverse("Hello World");
		System.out.println(v);
		System.out.println(sum(6));
	}
}