I'm not sure what I am doing wrong

using System.Collections.Generic;
namespace Treehouse.CodeChallenges
{
    public class Course
    {
        //  Compiler complains: error CS1520: Class, struct, or interface method must have a return type
        public Students()

        {
            Students = new List<Student>();
            }
        public int Id { get; set; }
        public int TeacherId { get; set; }
        public string Title { get; set; }
        public string Description { get; set; }
        public int Length { get; set; }
        public Teacher Teacher { get; set; }

        public ICollection<Student> Students { get; set; }
    }
}

namespace Treehouse.CodeChallenges
{
    public class Student
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}