#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const int N = 20;

int n, ans;
char s[N];

int main() {
    scanf("%s", s + 1);
    n = strlen(s + 1);

    ans = 0;
    for (int i = 1, cnt = 0; i <= n; ++i) {
        if (s[i] == 'A') {
            ans += i - 1 - cnt;
            ++cnt;
        }
    }
    printf("%d\n", ans);

    return 0;
}