Reverse string program in C#

using System;
class ReverseStr {
  public static void Main() {
      string str,revStr="";
      int len;
      Console.WriteLine("Enter the String: ");
      str=Console.ReadLine();
      len=str.Length-1;
      while(len>=0)
      {
          revStr=revStr+str[len];
          len--;
      }
      Console.WriteLine("Reverse String are:"+revStr);
  }
}