using System;

using System.Text;                  

public class Program

{

    public static void Main(string str)

    {

        str= "Hello Nikhil";

        int Start= str.Length-1;

        int End = str.Length-1;

        StringBuilder Rev= new StringBuilder();

        int i;

        while (Start > 0)

        {

            if (str[Start]==' ')

            {

                i= Start+1;

                while(i<=End)

                {

                Rev.Append(str[i]);

                    i++;

                }

                Rev.Append(' ');

                End= Start-1;

            }

            Start--;

        }

        for(i=0; i<=End; i++)

        {

            Rev.Append(str[i]);

        }

        Console.WriteLine(Rev);

    }

    }

​