StudentAcademy*

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

namespace StudentAcademy
{
    class Program
    {
        static void Main(string[] args)
        {
            var studentsGradesDictionary = new Dictionary<string, List<double>>();
            int nPairOfRows = int.Parse(Console.ReadLine());
            for (int i = 0; i < nPairOfRows; i++)
            {
                string student = Console.ReadLine();
                double grade = double.Parse(Console.ReadLine());
                if (studentsGradesDictionary.ContainsKey(student) == false)
                {
                    studentsGradesDictionary[student] = new List<double>();
                    studentsGradesDictionary[student].Add(grade);
                }

                else
                {
                    studentsGradesDictionary[student].Add(grade);
                }
            }

            foreach (var kvp in studentsGradesDictionary.Where(x=>x.Value.Average()>=4.50)
                     .OrderByDescending(x=>x.Value.Average()))
            {
                string student = kvp.Key;
                var listGrades = kvp.Value;
                double averageGrade = listGrades.Average();
                Console.WriteLine($"{student} -> {averageGrade:F2}");
            }
        }
      }
    }