#include <iostream>
#include <stdio.h>
#include <string>
#include <list>
#include <vector>
#include <algorithm>

#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;//print
typedef long long ll;
using namespace std;


int main(){
    cin.tie(0);
   	ios::sync_with_stdio(false);
    
    string s;
    cin >> s;
    int a = 0;
    int ans = 0;
    rep(i,s.length()){
        if(s[i]=='A'){
            ans = ans+i-a;
            a+=1;
        }
    }
    P(ans);
    return 0;
}