#line 2 "/home/cocojapanpan/Procon_CPP/proconLibrary/lib/template/procon.hpp"

#ifndef DEBUG
// 提出時にassertはオフ
#ifndef NDEBUG
#define NDEBUG
#endif
// 定数倍高速化
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#endif

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

#define ALL(x) (x).begin(), (x).end()
template <class T>
using vec = vector<T>;
template <class T, class S>
inline bool chmax(T &a, const S &b) {
    return (a < b ? a = b, 1 : 0);
}
template <class T, class S>
inline bool chmin(T &a, const S &b) {
    return (a > b ? a = b, 1 : 0);
}
template <class T>
constexpr T INF = 1'000'000'000;
template <>
constexpr int INF<int> = 1'000'000'000;
template <>
constexpr ll INF<ll> = ll(INF<int>) * INF<int> * 2;
#line 2 "main.cpp"

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int N;
    cin >> N;
    string S;
    cin >> S;
    // 左右から貪欲に
    // 自分より左のAの数と、自分より右のCの数を高速に求めたい
    // '?'はワイルドカード扱いで...
    vec<int> leftA(N), rightC(N);
    for(int i = 1; i < N; i++) {
        if(S[i - 1] != 'C') {
            leftA[i] = leftA[i - 1] + 1;
        } else {
            leftA[i] = leftA[i - 1];
        }
    }
    for(int i = N - 2; i >= 0; i--) {
        if(S[i + 1] != 'A') {
            rightC[i] = rightC[i + 1] + 1;
        } else {
            rightC[i] = rightC[i + 1];
        }
    }
    for(int i = 0; i < N; i++) {
        if(S[i] != '?') continue;
        if(leftA[i] < rightC[i]) S[i] = 'A';
        else S[i] = 'C';
    }
    int curACnt = 0;
    ll score = 0;
    for(int i = 0; i < N; i++) {
        if(S[i] == 'A') curACnt++;
        else score += curACnt;
    }
    cout << score << "\n";
}