package yuki172;

import java.util.Scanner;

public class B {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		sc.close();
		int bonus = 0;
		int ans = 0;
		for(int i=0; i<S.length(); i++) {
			if(S.charAt(i) == 'A') {
				ans += bonus;
			} else {
				bonus++;
			}
		}
		System.out.println(ans);
	}
}