New dynamic variable in C# 4.0

using System;
using System.Dynamic;
static class DyanmicDemo
{
    public static void Main() {
  for(Int32 demo =0; demo < 2; demo++) {
   dynamic arg = (demo == 0) ? (dynamic) 5 : (dynamic) "A";
   dynamic result = Plus(arg);
   M(result);
  }
 }
    private static dynamic Plus(dynamic arg) { return arg + arg; }
    private static void M(Int32 n) { Console.WriteLine("M(Int32): " + n); }
    private static void M(String s) { Console.WriteLine("M(String): " + s); }
}