#include <bits/stdc++.h>
using namespace std;

int main() {
    int dns_length;
    cin >> dns_length;

    string dns;
    cin >> dns;

    int count_A = 0;      // Count of 'A'
    int count_AG = 0;     // Count of 'AG'
    int found_dns = 0;    // Count of 'AGT'

    // Process the string in a single pass
    for (int i = 0; i < dns_length; i++) {
        if (dns[i] == 'T') {
            found_dns += count_AG; // Every 'AG' before this 'T' can form an 'AGT'
        } else if (dns[i] == 'G') {
            count_AG += count_A;  // Every 'A' before this 'G' can form an 'AG'
        } else if (dns[i] == 'A') {
            count_A++;            // Increment the count of 'A'
        }
    }

    cout << found_dns-1 << endl;

    return 0;
}