#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define CK(N, A, B) (A <= N && N < B)
#define REP(i, a, b) for (int i = a; i < b; i++)
#define RREP(i, a, b) for (int i = (b - 1); a <= i; i--)
#define F first
#define S second
#define ll long long

const int INF = 1e9;
const long long LLINF = 1e18;

using namespace std;

int dy[] = {0,1,0,-1};
int dx[] = {1,0,-1,0};
int dy8[] = {0,1,1,1,0,-1,-1,-1};
int dx8[] = {1,1,0,-1,-1,-1,0,1};

/*==================================================*/
/*variable*/
string S;
/*==================================================*/
/*function*/

/*==================================================*/

int main() {
    cin>>S;
    int cnt = 0;
    int ans = 0;
    bool flag = false;
    REP(i,0,S.size()){
        if(flag  && S[i] == 'A'){
            cnt++;
        }else{
            flag = false;

            if(S[i] == 'A'){
                ans += (i - cnt);
                cnt++;
            }
        }
    }
    cout<<ans<<endl;
    return 0;
}