using System;

namespace No559
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var S = Console.ReadLine();

            var ans = 0;
            var ca = 0;
            for (var i = 0; i < S.Length; i++)
            {
                if (S[i] != 'A') continue;
                ans += i - ca;
                ca++;
            }

            Console.WriteLine(ans);
        }
    }
}