using System;

using System.Linq;

using System.Text.RegularExpressions;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        while (true)

        {

            Console.WriteLine("\nEnter a word:");

            string input = Console.ReadLine();

            Regex regex = new Regex ("^[a-zA-Z]*$");

            var validInput = !string.IsNullOrEmpty(input) && regex.IsMatch(input);

            if (!validInput)

            {

                Console.WriteLine ("Invalid input");

            }

            else

            {

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

                foreach(char c in input)

                {

                    characterCounts.TryGetValue(c, out int charValue);

                    characterCounts[c] = charValue + 1;

                }

                foreach (var charCount in characterCounts)

                {

                    Console.WriteLine ($"Character: {charCount.Key} | Count: {charCount.Value}");

                }

            }

        }

    }

}