import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.next();

        int[] arr = new int[s.length()];
        int ans = 0, j = 0;
        for(int i=0; i<s.length(); i++) {
            if(s.charAt(i) == 'A') {
                arr[j] = i - j;
                ans += arr[j];
                j++;
            }
        }

        System.out.println(ans);
    }
}