Change Nums

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Numerics;
using System.Globalization;
using System.Net;

namespace ConsoleApplication3
{
    class Program
    {
        static double Sum(string n)
        {
            var alphabet = new List<char>{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u',
                            'v', 'w', 'x', 'y', 'z'};
            char first = n.ToCharArray()[0];
            char second = n.ToCharArray()[n.Length - 1];
            double num = double.Parse(n.Substring(1, n.Length - 2));

            if (char.IsUpper(first))
                num = num / (alphabet.IndexOf(char.ToLower(first)) + 1);
            else
                num = num * (alphabet.IndexOf(first) + 1);

            if(char.IsUpper(second))
                num = num - (alphabet.IndexOf(char.ToLower(second)) + 1);
            else
                num = num + (alphabet.IndexOf(second) + 1);

            return num;
        }

        static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split(new char[]{' '}, StringSplitOptions.RemoveEmptyEntries).ToArray();

            double result = 0;

            foreach (string i in input)
            {
                result += Sum(i);
            }

            Console.WriteLine("{0:F2}", result);
        }
    }
}