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

int main() {
	int n;
	cin >> n;
	string s;
	cin >> s;
	vector<long long> dp(2);
	for (int i = 0; i < n; i++){
		if (s[i] == 'A'){
			dp[0]++;
		}
		if (s[i] == 'C'){
			dp[1] += dp[0];
		}
	}
	long long ans = dp[1];
	long long r = count(s.begin(), s.end(), 'C') + count(s.begin(), s.end(), '?');
	long long l = 0;
	long long m = 0;
	if (count(s.begin(), s.end(), '?') == 0){
		cout << ans << endl;
		return 0;
	}
	for (int i = 0; i < n; i++){
		if (s[i] == 'C'){
			r--;
		}
		if (s[i] == 'A'){
			l++;
		}
		if (s[i] == '?'){
			r--;
			l++;
		}
		m = max(m, l * r);
	}
	ans += m;
	cout << ans << endl;
}