using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var csv = new string[] { "Amy", "Charlie", "Daron" };

        var database = new string[] { "Raul", "Jun", "Chris" };

        var input = new string[] { "Yvonne", "Theo", "Carla" };

        IEnumerable<string> AllStudents() 

        {

            foreach (var student in csv)

            {

                yield return student;   

            }

            foreach (var student in database)

            {

                yield return student;   

            }

            foreach (var student in input)

            {

                yield return student;   

            }           

        };

        foreach (var student in AllStudents()) 

        {

            Console.WriteLine(student); 

        }

    }

}