#include<iostream>
#include<iomanip>
#include<math.h>
#include<vector>
#include<algorithm>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<string>
#include<complex>
#include<random>
#include<time.h>

#define INF 1000000000ll
#define MOD 1000000007ll
#define EPS 1e-8

#define REP(i, m) for(long long i = 0; i < m; ++i)
#define FOR(i, n, m) for(long long i = n; i < m; ++i)
#define ALL(v) v.begin(), v.end()
#define pb push_back

using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
typedef long double ld;


int main() {
	ios::sync_with_stdio(false);
	string s;
	cin>>s;
	int ca=0,cb=0;
	REP(i,s.size()) {
		if(s[i]=='A') ++ca;
		else ++cb;
	}
	int cnt=0;
	int roc=0;
	int pos=0;
	while(roc<ca) {
		if(s[pos]=='A') {
			cnt+=pos-roc;
			++roc;
		}
		++pos;
	}
	cout<<cnt<<endl;
}