using System;
using System.Linq;
class Program {
    static void Main() {
        string s = Console.ReadLine();
        int cntA = s.Count(x => x == 'A');
        int ans = 0;
        for (int i = 0; i < cntA; i++) {
            if (s[i] == 'B') ans -= i;
        }
        for (int i = cntA; i < s.Length; i++) {
            if (s[i] == 'A') ans += i;
        }
        Console.WriteLine(ans);
    }
}