# -*- coding: utf-8 -*-
"""
No.559 swapAB列
https://yukicoder.me/problems/no/559

"""
import sys
from sys import stdin
input = stdin.readline


def check_A_positions(S):
    res = []
    for i, s in enumerate(S):
        if s == 'A':
            res.append(i)
    return res


def main(args):
    S = input().strip()
    res = check_A_positions(S)

    after_swap = (0 + len(res)-1) * len(res) // 2
    current = sum(res)
    print(current - after_swap)


if __name__ == '__main__':
    main(sys.argv[1:])