import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        char[] S = sc.next().toCharArray();

        int aCount = 0;
        int numSwap = 0;

        for (int i = 0; i < S.length; i++) {

            if (S[i] == 'A') {

                numSwap += i - aCount;
                aCount++;

            }

        }

        System.out.println(numSwap);

    }

}