#include <iostream>
#include <string>
using namespace std;
typedef long long lint;

#define MIN(a,b) ((a)<(b)?(a):(b))
#define MAX(a,b) ((a)>(b)?(a):(b))

int main()
{
	int a = 0, b = 0, cntA, ans = 0;
	string S;
	cin >> S;
	for (int i = 0; i < S.size(); i++) {
		if (S[i] == 'A') a++;
		else b++;
	}
	if (a * b == 0) {
		cout << 0 << endl;
		return 0;
	}
	cntA = -1;
	for (int i = 0; i < S.size(); i++) {
		if (S[i] == 'B') continue;
		cntA++;
		ans += i - cntA;
	}
	cout << ans << endl;
}