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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    string s, t = "AC{";
    cin >> s;
    auto f = [&](int mid){
        vector<array<ll,3>> dp(n + 1, {0, 0, 0});
        dp[0][0] = 1;
        for(int i = 0; i < n; i++){
            for(int j = 0; j < 3; j++){
                dp[i + 1][j] += dp[i][j];
                if(s[i] == '?'){
                    if(i < mid && j == 0) dp[i + 1][j + 1] += dp[i][j];
                    if(i >= mid && j == 1) dp[i + 1][j + 1] += dp[i][j];
                }else{
                    if(s[i] == t[j]) dp[i + 1][j + 1] += dp[i][j];
                }
            }
        }
        return dp[n][2];
    };
    ll ans = 0;
    int l = 0, r = n + 1, c1, c2;
    while(l + 3 < r){
        c1 = (2 * l + r) / 3;
        c2 = (l + 2 * r) / 3;
        ll v1 = f(c1), v2 = f(c2);
        ans = max(ans, max(v1, v2));
        if(v1 >= v2) r = c2;
        else l = c1;
    }
    for(int i = l - 10; i <= r + 10; i++){
        ans = max(ans, f(i));
    }
    l = 0, r = n + 1, c1, c2;
    while(l + 3 < r){
        c1 = (2 * l + r) / 3;
        c2 = (l + 2 * r) / 3;
        ll v1 = f(c1), v2 = f(c2);
        ans = max(ans, max(v1, v2));
        if(v1 > v2) r = c2;
        else l = c1;
    }
    for(int i = l - 10; i <= r + 10; i++){
        ans = max(ans, f(i));
    }
    cout << ans << '\n';
}