#include <stdio.h>
#include <algorithm>
#include <deque>
#include <string>
#include <iostream>
using namespace std;
using ll = long long;

void solve();
int main() {
	solve();
#ifdef DBG
	while (true);
#endif
}

//559
void solve() {
	char s[13];
	int costs = 0, count = 0;
	scanf("%s", s);
	for (int i = 0; s[i] != 0; i++) {
		if (s[i] == 'A')
			costs += count;
		if (s[i] == 'B')
			count++;
	}
	printf("%d\n", costs);
}