static void Main(string[] args)
        {
            Console.WriteLine("Please input the TXT file path in the next line");
            var input = Console.ReadLine();
            if (!string.IsNullOrEmpty(input) && File.Exists(input))
            {
                // Find the letter frequency
                var frequency = Encoding.UTF8.GetString(Encoding.Default.GetBytes(File.ReadAllText(input))).ToUpper()
                    .Where(c => Char.IsLetter(c))
                    .GroupBy(c => c)
                    .ToDictionary(g => g.Key, g => g.Count());
                // Print the total number of letters read
                Console.WriteLine("Total number of letters read: " + frequency.Sum(intValue => intValue.Value));
                // Order items in descending count value, only take the top 10 records
                foreach (var item in frequency.OrderByDescending(key => key.Value).Take(10))
                    Console.WriteLine(item.Key + " (" + item.Value + ")");
            }
            else
                Console.WriteLine("File does not exist or cannot be read.");
            Console.WriteLine("Please press the ENTER key to exit the application...");
            Console.ReadLine();
        }