using System;

using System.Collections.Generic;

public class Author

{

    public string FirstName

    {

        get;

        set;

    }

​

    public string LastName

    {

        get;

        set;

    }

}

​

public class Document

{

    public Document()

    {

        this.Authors = new List<Author>();

    }

​

    public string Title

    {

        get;

        set;

    }

​

    public string FilePath

    {

        get;

        set;

    }

​

    public List<Author> Authors

    {

        get;

        private set;

    }

}

​

public class Project

{

    public Project()

    {

        this.Documents = new List<Document>();

    }

​

    public string Name

    {

        get;

        set;

    }

​

    public DateTime CreationDate

    {

        get;

        set;

    }

​

    public List<Document> Documents

    {

        get;

        private set;

    }

}

​

public static class ProjectsExercise

{

    public static void Main()

    {

        Run();

    }

    public static void Run()

    {

        Project project = new Project();

​

        Author a = new Author() { FirstName = "a" };

        Author b = new Author() { FirstName = "b" };

        var d = new Document();

        var d2 = new Document();

        d.Authors.Add(a);

        d.Authors.Add(b);

        d2.Authors.Add(b);

        project.Documents.Add(d);

        project.Documents.Add(d2);

    }

​

    static int CountDocumentsByAuthor(Project project, Author author)

    {

        //Complete code here:

​

        throw new NotImplementedException();

    }

}