using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace YukiCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve();
        }

        public void Solve()
        {
            string s = Console.ReadLine();

            int sum = 0;
            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] == 'B')
                {
                    for (int j = i + 1; j < s.Length; j++)
                    {
                        if (s[j] == 'A') sum++;
                    }
                }

            }
            
            Console.WriteLine(sum);
            
        }
    }
}