#include "bits/stdc++.h"

using namespace std;
using ll = long long;
using IP = pair<int, int>;


#define INF 999999999
#define atcoder(int)1e9+7
#define Endl endl
#define all(v) (v.begin(),v.end())
#define pb(a) push_back(a)

int main() {
	
	string s;
	cin >> s;
	int ans = 0;
	int l = 0;
	for (int i = 0; i < s.length(); i++) {
		if (s[i] == 'A') {
			ans += i - l;
			l++;
		}
	}
	cout << ans << endl;
	
	return 0;
}