using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var dict = new Dictionary<string,string>();

        dict["test1"] = "123"; // Add

        dict["test2"] = "456"; // Add

        dict["test2"] = "abc"; // Update

        Console.WriteLine("test1: " + dict["test1"]);

        Console.WriteLine("test2: " + dict["test2"]);

    }

}