#include <iostream>
#include <string>
using namespace std;

int main() {
    long N;
    string dns;
    cin >> N >> dns;

    long szamlalo = 0;

    long i = 0;
    while (i < N) {
        if (dns[i] == 'A') {
            bool tartalmaz_g = false;
            long j = i + 1;
            while (j < N) {
                if (dns[j] == 'G') {
                    tartalmaz_g = true;
                }
                if (dns[j] == 'T' && tartalmaz_g) {
                    szamlalo++;
                    break;
                }
                j++;
            }
        }
        i++;
    }

    cout << szamlalo << endl;

    return 0;
}