using System;

using System.Collections.Generic;

using Newtonsoft.Json.Linq;

​

​

public class Program

{

    public static void Main()

    {

        Dictionary<string, bool> a = new Dictionary<string, bool>();

        String key = "ff";

        if(!a.ContainsKey(key)){

            a.Add(key,false);

        }

​

        a[key] = false;

        Console.WriteLine(a[key]);

    }

}