import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

s = S()
n = len(s)

cnt = 0
ans = 0
for i in range(n):
    if s[i] == 'A':
        ans += i-cnt
        cnt += 1

print(ans)