#include <iostream>
#include <cstdio>

using namespace std;

int n, cnt, ans;
string s;

int main() {
    // freopen("ab.in", "r", stdin);
    // freopen("ab.out", "w", stdout);

    cin >> s;

    n = s.size();
    s = ' ' + s;
    cnt = 1;
    for (int i = 1; i <= n; ++i) {
        if (s[i] == 'A') {
            if (cnt != i) {
                ans += i - cnt;
            }
            ++cnt;
        }
    }

    printf("%d\n", ans);

    return 0;
}