Прави си, благодаря! Заблудих се, защото в условите към Input е записано:

• There will be no case with 2 or more users with same total points!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection.Metadata;
using System.Reflection.Metadata.Ecma335;
using System.Security.Cryptography.X509Certificates;
using System.Threading;

namespace Sets_and_Dictioanries
{
    class Program
    {
        static void Main(string[] args)
        {
            var passwordsForContests = new Dictionary<string, string>();
            var contests = new SortedDictionary<string, Dictionary<string, int>>();
            var totalPoints = new Dictionary<string, int>();

            var bestPoints = int.MinValue;
            var bestUser = string.Empty;

            while (true)
            {
                var input = Console.ReadLine();
                if (input == "end of contests")
                {
                    break;
                }
                var inputParts = input.Split(":");

                var contest = inputParts[0];
                var password = inputParts[1];

                if (!contests.ContainsKey(contest))
                {
                    passwordsForContests[contest] = password;
                }

            }

            while (true)
            {
                var input = Console.ReadLine();
                if (input == "end of submissions")
                {
                    break;
                }
                var inputParts = input.Split("=>");
                var contest = inputParts[0];
                var password = inputParts[1];
                var username = inputParts[2];
                int points = int.Parse(inputParts[3]);


                if (!passwordsForContests.ContainsKey(contest) || !passwordsForContests.ContainsValue(password))
                {
                    continue;
                }
                else
                {
                    if (!contests.ContainsKey(username))
                    {
                        contests[username] = new Dictionary<string, int>();
                        contests[username].Add(contest, points);
                        totalPoints.Add(username, points);

                    }
                    else
                    {
                        if (contests[username].ContainsKey(contest))
                        {
                            if (contests[username][contest] < points)
                            {
                            contests[username][contest] = points;
                            totalPoints[username] += points;
                            }
                        }
                        else if (!contests[username].ContainsKey(contest))
                        {
                            contests[username].Add(contest, points);
                            totalPoints[username] += points;
                        }
                    }
                }
            }

            foreach (var points in totalPoints)
            {
                if (bestPoints < points.Value)
                {
                    bestPoints = points.Value;
                    bestUser = points.Key;
                }
            }

            Console.WriteLine($"Best candidate is {bestUser} with total {bestPoints} points.\nRanking:");

            foreach (var user in contests)
            {
                Console.WriteLine(user.Key);
                foreach (var contest in user.Value.OrderByDescending(x=>x.Value))
                {
                    Console.WriteLine($"#  {contest.Key} -> {contest.Value}");
                }
            }

        }
    }
}

Цял ден си блъсках главата и все 60/100. Малко помощ?