using System;
using System.Linq;
using System.Collections.Generic;

static class Program{
    static void Main(){
        new Magatro().Solve();
    }
}

class Magatro{
    private string S = Console.ReadLine();
    private void Scan(){
        
    }
    
    public void Solve(){
        Scan();
        int aCnt = 0;
        int anser =0;
        for(int i=0;i<S.Length;i++){
            if (S[i]=='A'){
                anser+=(i-aCnt);
                aCnt++;
            }
        }
        Console.WriteLine(anser);
    }
}