Phonebook and Phonebook Upgrade

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _12.Phonebook_Upgrade
{
    class Program
    {
        static void Main(string[] args)
        {
            var phonebook = new SortedDictionary<string, string>();
            string command = "";
            while (true)
            {
                string[] entry = Console.ReadLine().Split(' ').ToArray();
                command = entry[0];
                if (command == "END")
                {
                    break;
                }
                string name = "";
                string phone = "";

                if (entry.Length >= 2)
                {
                    name = entry[1];
                }

                if (entry.Length == 3)
                {
                    phone = entry[2];
                }

                if (command == "A")
                {
                    if (phonebook.ContainsKey(name) && !phonebook.ContainsValue(phone))
                    {
                        phonebook.Remove(name);
                        phonebook.Add(name, phone);
                    }
                    else if (!phonebook.ContainsKey(name) && !phonebook.ContainsValue(phone))
                    {
                        phonebook.Add(name, phone);
                    }
                }
                else if (command == "S")
                {
                    if (!phonebook.ContainsKey(name))
                    {
                        Console.WriteLine($"Contact {name} does not exist.");
                    }
                    else if (phonebook.ContainsKey(name))
                    {
                        foreach (var item in phonebook)
                        {
                            if (item.Key == name)
                            {
                                Console.WriteLine($"{item.Key} -> {item.Value}");
                            }
                        }
                    }
                }
                else if (command == "ListAll")
                {
                    foreach (var item in phonebook)
                    {
                        Console.WriteLine($"{item.Key} -> {item.Value}");
                    }

                }

            }
        }
    }
}