#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e18
#define f first
#define s second

mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());

void Solve() 
{
    int n; cin >> n;
    string s; cin >> s;
    
    int ans = 0;
    int at = 0;
    int a = 0, c = 0, t = 0;
    int good = 0;
    for (auto x: s){
        if (x == 'A') {
            a++;
        }
        else if (x == 'C'){
            c++;
            at += a;
        } 
        else {
            t++; good += a;
        } 
    }
    
    int ca = 0, cc = 0, ct = 0;
    int t1 = 0, t2 = t;
 //   cout << good << "\n";
    ans = max(ans, good + t1 * (c - cc) + t2 * ca + t1 * t2);
    for (auto x: s){
        if (x == 'A'){ ca++; good -= (t - ct); }
        else if (x == 'C'){ cc++; good += ct;}
        else {ct++;}
        
        t1 = ct;
        t2 = (t - ct);
       // cout << good << "\n";
        ans = max(ans, good + t1 * (c - cc) + t2 * ca + t1 * t2);
    }
    
    cout << ans + at << "\n";
}

int32_t main() 
{
    auto begin = std::chrono::high_resolution_clock::now();
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
 //   cin >> t;
    for(int i = 1; i <= t; i++) 
    {
        //cout << "Case #" << i << ": ";
        Solve();
    }
    auto end = std::chrono::high_resolution_clock::now();
    auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
   // cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n"; 
    return 0;
}