import java.util.*;

public class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args) {
		String s = sc.next();
		int[] ar = new int[s.length()];
		
		int j = 0;
		int total = 0;
		for (int i=0; i<s.length(); i++) {
			if (s.charAt(i)=='A') {
				ar[j] = i-j;
				total += ar[j];
				j++;
			}
		}
		System.out.println(total);
	}
}