import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	char[] arr = sc.next().toCharArray();
        long total = 0;
        int bCount = 0;
        for (char c : arr) {
            if (c == 'A') {
                total += bCount;
            } else {
                bCount++;
            }
        }
    	System.out.println(total);
	}
}