#include <bits/stdc++.h>
using namespace std;

int main() {
	long long N; cin >> N;
	string S; cin >> S;

	int a_count = 0, c_count = 0;
	for (int i = 0; i < N; i++) {
		if (S[i] == 'C' || S[i] == '?') c_count++;
	}

	for (int i = 0; i < N; i++) {
		if (S[i] == 'A') a_count++;
		if (S[i] == 'C') c_count--;
		if (S[i] == '?') {
			if (a_count >= c_count) S[i] = 'C';
			else {
				S[i] = 'A';
				a_count++;
			}
			c_count--;
		}
	}

	long long now = 0;
	long long ans = 0;
	for (int i = 0; i < N; i++) {
		if (S[i] == 'A') now++;
		else ans += now;
	}

	cout << ans << endl;
}