import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import static java.lang.System.in;

public class No559 {
    public static void main(String[] args) throws IOException {

        BufferedReader reader = new BufferedReader(new InputStreamReader(in));

        int numOfB = 0;

        String S = reader.readLine();

        int counter = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) == 'A') {
                counter += numOfB;
            } else {
                numOfB += 1;
            }
        }

        System.out.println(counter);

    }
}