package m.shin;
import java.util.Scanner;
public class Con559 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String str = s.nextLine();
		s.close();

		int count = 0 , b = 0;
		for(int i = 0;i < str.length();i++){
			if(str.charAt(i) == 'A'){
				count += b;
			}else{
				b++;
			}
		}
		System.out.println(count);

	}

}