01. Value of a String

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

namespace Extended
{


    class Program
    {
        static bool IsLetter(string str)
        {
            for (int i = 0; i < str.Length; i++)
            {
                if ((int)str[i] >= 65 && (int)str[i] <= 90 ||
                    (int)str[i] >= 97 && (int)str[i] <= 122)
                {
                    return true;
                }
            }
                return false;
        }


        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            string upOrLower = Console.ReadLine();
            List<char> ch = new List<char>();
            ch = input.ToList();
            int sum = 0;
            if (upOrLower == "UPPERCASE")
            {
                for (int i = 0; i < input.Length; i++)
                {
                    if (IsLetter(input) && char.IsUpper(input[i]))
                    {
                        sum += (int)input[i];
                    }
                }

            }
            else
            {
                for (int i = 0; i < input.Length; i++)
                {
                    if (IsLetter(input) && char.IsLower(input[i]))
                    {
                        sum += (int)input[i];
                    }
                }

            }

            Console.WriteLine("The total sum is: {0}", sum);
        }

    }
}