#include <iostream>
#include <string>
using namespace std;
using ll = long long;
int main () {
    int N;
    cin >> N;
    ll cnt[3][200020];
    for (int i = 0; i < 3; i ++) cnt[i][0] = 0;
    int A[200020];
    string key = "AC?";
    for (int i = 0; i < N; i ++) {
        char c;
        cin >> c;
        for (int j = 0; j < 3; j ++) {
            cnt[j][i + 1] = cnt[j][i];
            if (key[j] == c) {
                cnt[j][i + 1] ++;
                A[i] = j;
            }
        }
    }
    ll sum = 0;
    for (int i = 0; i < N; i ++) {
        if (A[i]) {
            sum += cnt[0][i];
        }
    }
    ll ans = sum;
    for (int i = 0; i < N; i ++) {
        if (A[i] == 2) {
            sum -= cnt[0][i] + cnt[2][i];
            sum += cnt[1][N] + cnt[2][N] - (cnt[1][i + 1] + cnt[2][i + 1]);
        }
        ans = max(ans, sum);
    }
    cout << ans << endl;
}