#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    string s;
    cin >> n >> s;
    vector<int> dp(n);
    int k = 0;
    int db = 0;
    for (int i = n - 1; i >= 0; i --) {
        if (s[i] == 'T') k += 1;
        dp[i] = k;
    }
    for (int i = 0; i < n; i ++) {
        if (s[i] == 'A') {
            for (int j = i; j < n; j ++) {
                if (s[j] == 'G') {
                    db += dp[j];
                    break;
                }
            }
        }
    }
    cout << db;
    return 0;
}