//#pragma GCC target("avx")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

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

//local debug
#ifdef LOCAL
#include <debug_print.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif

#define overload4(a, b, c, d, e, ...) e

//alias
using ll = long long;
using ull = unsigned long long;
using ld = long double;

//constants
constexpr const int MOD = 998244353;
constexpr const int MODM = 1000000007;
struct {template <class T> constexpr operator T(){return std::numeric_limits<T>::max();}} INF;
struct {template <class T> constexpr operator T() {return std::numeric_limits<T>::lowest();}} MINF;

//rep(for-loop) macro
#define rep2(i, n) for(ll i = 0; i < n; i++)
#define rep3(i, k, n) for(ll i = k; i < n; i++)
#define rep4(i, k, n, a) for(ll i = k; i < n; i += a)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2)(__VA_ARGS__)
#define rep1_2(i, n) for(ll i = 1; i <= n; i++)
#define rep1_3(i, k, n) for(ll i = k; i <= n; i++)
#define rep1_4(i, k, n, a) for(ll i = k; i <= n; i += a)
#define rep1(...) overload4(__VA_ARGS__, rep1_4, rep1_3, rep1_2)(__VA_ARGS__)
#define Rep2(i, n) for(ll i = n - 1; i >= 0; i--)
#define Rep3(i, k, n) for(ll i = n - 1; i >= k; i--)
#define Rep4(i, k, n, a) for(ll i = n - 1; i >= k; i -= a) 
#define Rep(...) overload4(__VA_ARGS__, Rep4, Rep3, Rep2)(__VA_ARGS__)
#define Rep1_2(i, n) for(ll i = n; i >= 1; i--)
#define Rep1_3(i, k, n) for(ll i = n; i >= k; i--)
#define Rep1_4(i, k, n, a) for(ll i = n; i >= k; i -= a) 
#define Rep1(...) overload4(__VA_ARGS__, Rep1_4, Rep1_3, Rep1_2)(__VA_ARGS__)

//vector
#define vvecc(T, name, n, m) vector<vector<T>> name(n, vector<T>(m))
#define vvec(T, name, n) vector<vector<T>> name(n)
#define vvecs(T, name, n, m, s) vector<vector<T>> name(n, vector<T>(m, s))
#define all(x) begin(x), end(x)
#define MIN(v) *min_element(all(v))
#define MINI(v) distance(v.begin(), min_element(all(v)))
#define MAX(v) *max_element(all(v))
#define MAXI(v) distance(v.begin(), max_element(all(v)))
#define LB(v, x) distance((v).begin(), lower_bound(all(v), (x)))
#define UB(v, x) distance((v).begin(), upper_bound(all(v), (x)))
#define eb emplace_back
#define pb pop_back
template <class T> bool vec_same(vector<T> &a, vector<T> &b) {return (a.size() == b.size() && equal(all(a), b.begin()));}

//data structure macro
#define mp make_pair
#define fi first
#define se second
#define pq(T) priority_queue<T>
#define pqmin(T) priority_queue<T, vector<T>, greater<T>>
#define pqminp(T1, T2) priority_queue<pair<T1, T2>, vector<pair<T1, T2>>, greater<pair<T1, T2>>>

//output
#define pl() cout << '\n'
template<class T> void print(const T& a) {cout << a;}
void printl(){}
template<class T> void printl(const T& t){print(t); pl();}
template<class Head, class... Tail> void printl(const Head& head, const Tail&... tail) {print(head); cout << " "; printl(tail...);}
#define printd(x, d) cout << fixed << setprecision(d) << x << '\n'
template <class T> void print_vec(vector<T> v) {for(T x : v) cout << x << " "; pl();}
void Yes(bool a) {cout << (a ? "Yes" : "No") << '\n';}
void Out2(bool a, string yes, string no) {cout << (a ? yes : no) << '\n';}

//functions
int ctoll(char c) {return c - '0';}
char to_char(int x) {return x + '0';}
template<class T> bool check_bit(T tar, T bit) {return ((tar & (int)Epow(2, bit)) != 0);}
template<class... T> constexpr auto Emin(T... a){return min(initializer_list{a...});}
template<class... T> constexpr auto Emax(T... a){return max(initializer_list{a...});}
template<class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, const T &b) { if (a > b) { a = b; return true; } return false; }
template<class T> bool overflow_if_add(T a, T b) {return (std::numeric_limits<T>::max() - a) < b;}
template<class T> bool overflow_if_mul(T a, T b) {return (std::numeric_limits<T>::max() / a) < b;}
template<class T> ll Epow(T x, T y) {ll ans = 1; for(int i = 0; i < y; i++) ans *= x; return ans;}

//---------------------------------------------------------------------------------------------------
int main() {

    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(10);

    int N;
    cin >> N;
    string S;
    cin >> S;

    string base = S;

    rep(i, S.size()) {
        if(S[i] == '?')
        S[i] = 'A';
    }

    debug(S);
    vector<int> imosA(N + 2, 0), imosC(N + 2, 0);
    rep(i, S.size()) {
        if(S[i] == 'A') {
            imosA[i + 2]++;
            imosA[N + 1]--;
        }
        else if(S[i] == 'C') {
            imosC[0]++;
            imosC[i + 1]--;
        }
    }

    vector<int> Ax(N + 2, 0), Cx(N + 2, 0); //Ax[i] : i文字より左に何個Aがあるか(初期状態) Cx[i] : i文字目より右に何個Cがあるか(初期状態)
    Ax[0] = imosA[0];
    Cx[0] = imosC[0];
    rep1(i, N + 1) {
        Ax[i] = Ax[i - 1] + imosA[i];
        Cx[i] = Cx[i - 1] + imosC[i];
    }

    debug(Ax, Cx);

    ll ans = 0;
    rep(i, N) {
        if(S[i] == 'A')
        ans += Cx[i + 1];
    }

    debug(ans);

    int effective_Cx = 0;
    ll cur = ans;
    Rep(i, N) {
        if(S[i] == 'A' && base[i] == '?') {
            cur += Ax[i + 1];
            cur -= effective_Cx;
            effective_Cx++;
        }
        else if(S[i] == 'C') {
            effective_Cx++;
        }

        ans = max(ans, cur);
    }

    printl(ans);
}