#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
using namespace std;

int main() {
    int ans=0,c=0;
    string s; cin >> s;
    rep(i,0,s.size()){
        if(s[i] == 'A'){
            ans = i-c;
            c++;
        }
    }
    cout << ans << endl;
}