#pragma GCC target("avx2") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include // #include using namespace std; // using namespace atcoder; typedef long long ll; #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--) #define repk(i, k, n) for (int i = k; i < (int)(n); i++) #define all(v) v.begin(), v.end() #define mod1 1000000007 #define mod2 998244353 #define mod3 100000007 #define vi vector #define vs vector #define vc vector #define vl vector #define vb vector #define vvi vector> #define vvc vector> #define vvl vector> #define vvb vector> #define vvvi vector>> #define vvvl vector>> #define pii pair #define pil pair #define pli pair #define pll pair #define vpii vector> #define vpll vector> #define vvpii vector>> #define vvpll vector>> template void debug(T e){ cerr << e << endl; } template void debug(vector &v){ rep(i, v.size()){ cerr << v[i] << " "; } cerr << endl; } template void debug(vector> &v){ rep(i, v.size()){ rep(j, v[i].size()){ cerr << v[i][j] << " "; } cerr << endl; } } template void debug(vector> &v){ rep(i,v.size()){ cerr << v[i].first << " " << v[i].second << endl; } } template void debug(set &st){ for (auto itr = st.begin(); itr != st.end(); itr++){ cerr << *itr << " "; } cerr << endl; } template void debug(multiset &ms){ for (auto itr = ms.begin(); itr != ms.end(); itr++){ cerr << *itr << " "; } cerr << endl; } template void debug(map &mp){ for (auto itr = mp.begin(); itr != mp.end(); itr++){ cerr << itr->first << " " << itr->second << endl; } } void debug_out(){ cerr << endl; } template void debug_out(Head H, Tail... T){ cerr << H << " "; debug_out(T...); } ll my_pow(ll x, ll n, ll mod){ // 繰り返し二乗法.x^nをmodで割った余り. ll ret; if (n == 0){ ret = 1; } else if (n % 2 == 1){ ret = (x * my_pow((x * x) % mod, n / 2, mod)) % mod; } else{ ret = my_pow((x * x) % mod, n / 2, mod); } return ret; } ll inv(ll x, ll mod){ return my_pow(x, mod - 2, mod); } int main(){ ll N; cin >> N; string S; cin >> S; vl sum_a(N + 1); vl sum_c(N + 1); for (ll i = 0; i < N; i++){ if (S[i] == 'A') sum_a[i + 1] = sum_a[i] + 1; else sum_a[i + 1] = sum_a[i]; if (S[i] == 'C') sum_c[i + 1] = sum_c[i] + 1; else sum_c[i + 1] = sum_c[i]; } //debug(sum_a); //debug(sum_c); ll ans = 0; vl a_prd(N, 0); vl c_prd(N, 0); for (ll i = 0; i < N; i++){ if (S[i] == '?') a_prd[i] = sum_c[N] - sum_c[i]; if (S[i] == '?') c_prd[i] = sum_a[i + 1]; } ll hatena = 0; for (ll i = 0; i < N; i++){ if (S[i] == '?') hatena++; } //debug(a_prd); //debug(c_prd); vl a_prd_sum(N, 0); vl c_prd_sum(N, 0); a_prd_sum[N - 1] = a_prd[N - 1]; c_prd_sum[0] = c_prd[0]; for (ll i = 0; i < N - 1; i++){ c_prd_sum[i + 1] = c_prd_sum[i] + c_prd[i + 1]; } for (ll i = N - 2; i >= 0; i--){ a_prd_sum[i] = a_prd_sum[i + 1] + a_prd[i]; } //debug(a_prd_sum); //debug(c_prd_sum); vl hatenas(0); rep(i,N){ if (S[i] == '?') hatenas.push_back(i); } ll ans_base = 0; ll a = 0; for (ll i = 0; i < N; i++){ if (S[i] == 'A') a++; if (S[i] == 'C') ans_base += a; } ans = max(ans, ans_base); //debug(ans_base); for (ll i = 0; i <= hatena; i++){ // どこまでを A で埋めるか if (i == 0){ // すべて C ll anssub = 0; anssub += c_prd_sum[N - 1]; ans = max(ans, anssub + ans_base); } else if (i == hatena){ // すべて A ll anssub = 0; anssub += a_prd_sum[0]; ans = max(ans, anssub += ans_base); } else{ ll anssub = 0; anssub += (a_prd_sum[0] - a_prd_sum[hatenas[i]]); anssub += (c_prd_sum[N - 1] - c_prd_sum[hatenas[i - 1]]); anssub += i * (hatena - i); ans = max(ans, anssub += ans_base); } } cout << ans << endl; }