#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;
#ifdef _WIN32
#include <Windows.h>
#endif

int main()
{
    string s;
    int bcnt = 0, tcnt = 0;;
    cin >> s;
    for (int i = 0; i < s.size(); i++){
        if (s[i] == 'B') bcnt++;
        if (s[i] == 'A') tcnt += bcnt;
    }
    cout << tcnt << endl;
}