Excel Columns

using System;

class ExcelColumns
{
    static void Main()
    {
        // input
        int n = int.Parse(Console.ReadLine());
        char identifier = new char();
        long result = 0;
        for (int i = n; i > 0; i--)
        {
            identifier = char.Parse(Console.ReadLine());

            if (i == 1)
            {
                result += (long)(identifier - 'A' + 1);
            }
            else
            {
                result += (long)(identifier - 'A' + 1) * (long)Math.Pow(26, i - 1);
            }
        }
        Console.WriteLine(result);
    }
}