#include<iostream>
#include<string>

using namespace std;

string a;

int swap(int n,int i){
	n++;
	char j = a[i];
	a[i] = a[i+1];
	a[i+1] = j;
	return n;
}

int inssort(){
	int num = 0;
	for(int i = 1; i < a.size(); i++){
		if(a[i] == 'A'){
			for(int j = i; j > 0 && a[j-1] != 'A' ; j--){
				num = swap(num,j-1);
			}
		}
	}
	return num;
}
				
		

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	
	cin >> a;
	int result;
	result = inssort();
	cout << result;
	return 0;
}