package net.ipipip0129.yukicoder.no559;

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String line = scan.nextLine();
		
		scan.close();
		
		int acnt = 0;
		int swapcnt = 0;
		
		for (int i = line.length() - 1; 0 <= i; i--) {
			switch (line.charAt(i)) {
			case 'A':
				acnt++;
				break;
			case 'B':
				swapcnt += acnt;
				break;
			}
		}
		
		System.out.println(swapcnt);
	}
}