#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <random>
#include <cassert>
#include <cstring>
using namespace std;

#define GET_ARG(a,b,c,F,...) F
#define REP3(i,s,e) for (i = s; i <= e; i++)
#define REP2(i,n) REP3 (i,0,(int)(n)-1)
#define REP(...) GET_ARG (__VA_ARGS__,REP3,REP2) (__VA_ARGS__)
#define RREP3(i,s,e) for (i = s; i >= e; i--)
#define RREP2(i,n) RREP3 (i,(int)(n)-1,0)
#define RREP(...) GET_ARG (__VA_ARGS__,RREP3,RREP2) (__VA_ARGS__)
#define DEBUG(x) cerr << #x ": " << x << endl

int toL[12];

int main(void) {
    string s;
    cin >> s;
    int i;
    REP (i,s.size()) {
        if (i > 0) toL[i] = toL[i-1];
        toL[i] += s[i] == 'B';
    }
    int ans = 0;
    REP (i,s.size()) if (s[i] == 'A') {
        ans += toL[i];
    }
    cout << ans << endl;
    return 0;
}