Courses - Dictionaries

using System;
using System.Linq;
using System.Collections.Generic;

public class Program
{
	public static void Main()
	{
		Dictionary<string,List<string>> coursesAndStudents = new Dictionary<string,List<string>>();

		while(true)
		{
			string command = Console.ReadLine();

			if (command == "end")
			{
				break;
			}

			string[] tokens = command.Split(':').Select(s => s.Trim()).ToArray();

			string courseName = tokens[0];
			string studentName = tokens[1];

			if (!coursesAndStudents.ContainsKey(courseName))
			{
				coursesAndStudents.Add(courseName, new List<string>());
				coursesAndStudents[courseName].Add(studentName);
			}
			else
			{
				coursesAndStudents[courseName].Add(studentName);
			}
		}

		foreach (var kvp in coursesAndStudents.OrderByDescending(x=>x.Value.Count))
		{
			Console.WriteLine("{0}: {1}",kvp.Key,kvp.Value.Count());

			foreach (var name in kvp.Value.OrderBy(n=>n))
			{
				Console.WriteLine("-- {0}",name);
			}
		}
	}
}