using System;
namespace ExtensionDemo
{
    static class StringExtension
    {
        public static int ToInteger(this string val)
        {
            return Convert.ToInt32(val);
        }
    }
}

using System;
using ExtensionDemo;
namespace ExtensionDemo
{
    class Class1
    {
        static void Main(string[] args)
        {
            string dem = "100";
            int a = dem.ToInteger();
            Console.WriteLine(a);
        }
    }
}