using System;
using System.Linq;

class No559
{
    static void Main()
    {
        var str = Console.ReadLine();
        var letterCount = str.Count(x => x == 'A');
        var place = 0;
        for (int i = 0; i < letterCount; ++i) place += i;
        var letterIndexCount = str.Where(x => x == 'A').Select((x, index) => index).Sum();
        Console.WriteLine(letterIndexCount - letterCount);
    }
}