using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var id = 1;

        List<UserCourse> userCourses = new List<UserCourse>();

        var result = (from uc in userCourses

                     where uc.Cource.Id == id

                     select uc.User).ToList();

        Console.WriteLine("Result: " + result.Count);

    }

}

​

class User {

    public int Id { get; set; }

    public string Username { get; set; }

    public string Password { get; set; }

}

​

class UserCourse {

    public User User { get; set; }

    public Course Cource { get; set; }

}

​

class Course {

    public int Id { get; set; }

    public string Name { get; set; }

}