mentorgroup

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;

public class Program
{
    const string DateFormat = "dd/MM/yyyy";
    const string DatesEnd = "end of dates";
    const string CommentsEnd = "end of comments";

    static void Main()
    {
        SortedDictionary<string, Student> studentGroup = new SortedDictionary<string, Student>();

        string input;

        while ((input = Console.ReadLine()) != DatesEnd)
        {
            string[] tokens = input?.Split().ToArray();
            string studentName = tokens[0];
            bool studentAttendance = tokens.Length > 1;

            Student student = new Student(studentName);

            if (!studentGroup.ContainsKey(studentName))
            {
                studentGroup.Add(studentName, student);
            }

            if (!studentAttendance) continue;
            string[] dates = tokens[1].Split(',').ToArray();
            foreach (string date in dates)
            {
                DateTime currentDate = DateTime.ParseExact(date, DateFormat, CultureInfo.InvariantCulture);
                studentGroup[studentName].Attendance.Add(currentDate);
            }
        }

        while ((input = Console.ReadLine()) != CommentsEnd)
        {
            string[] inputTokens = input?.Split('-').ToArray();
            string studentName = inputTokens[0];
            if (!studentGroup.ContainsKey(studentName)) continue;
            string comment = inputTokens[1];
            studentGroup[studentName].Comments.Add(comment);
        }

        foreach (var s in studentGroup)
        {
            Console.WriteLine(s.Value.ToString());
        }


    }
    public class Student
    {
        public Student(string name)
        {
            Name = name;
            this.Comments = new List<string>();
            this.Attendance = new List<DateTime>();
        }

        public string Name { get; set; }
        public List<string> Comments { get; set; }
        public List<DateTime> Attendance { get; set; }

        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();
            List<DateTime> orderedDates = this.Attendance.OrderBy(s => s).ToList();

            sb.AppendLine(this.Name)
                .AppendLine("Comments:");
            foreach (string c in this.Comments)
            {
                sb.AppendLine($"- {c}");
            }

            sb.AppendLine("Dates attended:");
            foreach (DateTime d in orderedDates)
            {
                sb.AppendLine($"-- {d.ToString(DateFormat)}");
            }
            return sb.ToString().TrimEnd();

        }
    }
}