using System;

using System.Collections.Generic;

using System.Linq;

​

public class Session{

    enum mark: int {

        not_passed = -1

    }

    //surname subjectName mark

    private Dictionary<string,Dictionary<string,int>> studentsMap;

    public Session(Dictionary<string,Dictionary<string,float>> list){

    }

    public List<string> getAllNotPassed(){

        return studentsMap.Where(x => x.Value.Any(y => y.Value == (int)mark.not_passed)).Select(x => x.Key).ToList();

    }

}

public class Program

{

    public static void Main()

    {   

        Session f = {"Пупкин",{"Матан",2}};

        Console.WriteLine("Hello World");

    }

}