courses

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

namespace mid_exam
{
    class Program
    {
        static void Main(string[] args)
        {
            var command = Console.ReadLine().Split(" : ").ToArray();

            var courses = new Dictionary<string, List<string>>();

            while (command[0] != "end")
            {
                if (!courses.ContainsKey(command[0]))
                {
                    courses.Add(command[0], new List<string>());
                }

                courses[command[0]].Add(command[1]);

                command = Console.ReadLine().Split(" : ").ToArray();
            }

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

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