using System;

using System.Linq;

​

namespace _1

{

    class Program

    {

        static void Main(string[] args)

        {

            Console.Write("Строка: ");

            string str = Console.ReadLine();

            string result = null;

            int counter = 1;

            string temp = null;

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

            {

                if (str[i].ToString() == temp)

                {

                    counter++;

                }

                else

                {

                    if (i > 0)

                    {

                        result += $"{temp}{counter}";

                        counter = 1;

                    }

                }

                if (i == str.Length - 1)

                {

                    result += $"{str[i]}{counter}";

                }

                temp = str[i].ToString();

            }

            Console.WriteLine(result);

            Console.ReadKey();

        }

    }

}

​