#include <list>
#include <iostream>
#include <vector>
#include <bitset>
#include <algorithm>

using namespace std;

int main() {

    int n;
    cin >> n;

    int n_invalid_a = 0;
    int n_valid_a = 0;
    int sol = 0;

    for (int i = 0; i < n; i++) {
        char base;
        cin >> base;

        switch (base)
        {
        case 'A':
            n_invalid_a++;
            break;
        case 'G':
            n_valid_a += n_invalid_a;
            n_invalid_a = 0;
            break;
        case 'T':
            sol += n_valid_a;
            break;
        default:
            break;
        }
    }

    cout << sol;

    return 0;
}