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

int main() {
    ios::sync_with_stdio(false);
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    
    int n = 0, sum = 0;
    cin >> n;
    string p;
    cin >> p;

    vector<int> gutan(n, 0);
    
    int ts = 0;
    for(int i = n-1; i >= 0; i--) {
        if (p[i] == 'T') {
            ts++;
        } else if (p[i] == 'G') {
            gutan[i] = ts;
            ts = 0;
        }
    }

    for(int i = 0; i < n; i++) {
        if (p[i] == 'A') {
            for(int j = i+1; j < n; j++) {
                sum += gutan[j];
            }
        }
    }

    //for(auto i : gutan) cerr << i;
    
    cout << sum << '\n';
    return 0;
}