#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <atcoder/modint>
using namespace std;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(int i=0; i<(int)(n); i++)
const i64 INF = 1001001001001001001;

using Modint = atcoder::static_modint<998244353>;

int main(){
    int N; cin >> N;
    string S; cin >> S;
    vector<int> Acnt(N+1, 0);
    vector<int> Ccnt(N+1, 0);
    rep(i,N) Acnt[i+1] = Acnt[i] + (S[i] != 'C' ? 1 : 0);
    rep(i,N) Ccnt[N-i-1] = Ccnt[N-i] + (S[N-i-1] != 'A' ? 1 : 0);
    rep(i,N) if(S[i] == '?'){
        if(Acnt[i] > Ccnt[i+1]) S[i] = 'C'; else S[i] = 'A';
    }
    i64 a = 0, ac = 0;
    for(char c : S){
        if(c == 'C') ac += a;
        if(c == 'A') a += 1;
    }
    cout << ac << endl;
    return 0;
}



struct ios_do_not_sync{
    ios_do_not_sync(){
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} ios_do_not_sync_instance;