using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Dictionary<string, string> iller = new Dictionary<string, string>()

        {

            {"1", "Istanbul"},

            {"2", "Ankara"},

            {"3", "Ezmir"},

            {"4", "Sakarya"}

        };

        //Ankara Kodu Kacdir?

        string illerAdi = "Ankara";

        var plakaKodu = iller.FirstOrDefault(x => x.Value == illerAdi).Key;

        Console.WriteLine(plakaKodu);

    }

}