using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Dictionary<string, string> dict = new Dictionary<string, string> { {"abc", "1"}, {"def", "2"} };

        foreach(var val in dict){

            if(val.Value == "2"){

                dict.Remove("def");

            }

        }

    }

}