#include <bits/stdc++.h>
using namespace std;
using LL = long long;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    string s;
    cin >> n >> s;
    LL ans = 0, c = 0;
    for (int i = 0, a = 0; i < n; i += 1) {
        if (s[i] == 'A') {
            a += 1;
        } else {
            c += 1;
            ans += a;
        }
    }
    for (int i = 0, a = 0; i < n; i += 1) {
        if (s[i] != 'A') {
            c -= 1;
        }
        if (s[i] == '?') {
            ans += max(c - a, 0LL);
        }
        if (s[i] != 'C') {
            a += 1;
        }
    }
    cout << ans;
}