// yukicoder: No.559 swapAB列
// 2019.4.20 bal4u

#include <stdio.h>

char S[15], *p = S;

int main()
{
	int c, ans;
	scanf("%s", S);
	ans = c = 0; while (*p) {
		if (*p++ == 'A') ans += c;
		else c++;
	}
	printf("%d\n", ans);
	return 0;
}