using System;

using System.Linq;

using System.Collections.Generic;

​

namespace ConsoleApp12

{

    public class Program

    {

        public static void check(string s)

        {

            Dictionary<char, int> d = new Dictionary<char, int>();

            s.ToLower();

            for (int i = 0; i < s.Length; i++)

                if (!d.ContainsKey(s[i])) d.Add(s[i], 1);

                else d[s[i]]++;

            foreach (var i in d.OrderByDescending(key => key.Value))

                Console.WriteLine(i.Key + ": " + i.Value);

        }

​

        public static void Main(string[] args)

        {

            Console.Write("Введите текст: ");

            check(Console.ReadLine());

        }

    }

}