String Reverse in C#

class Program
{
static void Main(string[] args)
{    //for storing string value

    String str, Revstr = "";      

    //for counting length of Given string 

    int length;                    

    //showing message to user

    Console.WriteLine("Enter
a string:");
    //to allow user to input string

    str = Console.ReadLine();  

    //storing the length of given string

    length =
str.Length - 1;  
//loops the given string length

    while (length >= 0)                  

    {

   //performimg a reverse string according to length of given
string       
Revstr = Revstr + str[length];     
      
length--;

    }
    // displaying output to user
    Console.WriteLine("Reverse
string is {0}", Revstr);
    // to keep window

    Console.ReadLine();

}

}