using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

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

        d["A"] = new Dictionary<string, string>();

        d["A"]["B"] = "C";

        if (d.TryGetValue("A", out var b) && b.TryGetValue("B", out var c))

        {

            Console.WriteLine("{0}", c);

        }

    }

}