// Source: https://usaco.guide/general/io

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

int main() {
	int n;
	string s;
	cin >> n >> s;
	vector<int> tcount(n), nextg(n);
	int t = 0, g = -1;
	long long ans = 0;
	for (int i = n - 1; i >= 0; i--) {
		tcount[i] = t;
		nextg[i] = g;
		if (s[i] == 'G') g = i;
		if (s[i] == 'T') t++;
		if (s[i] == 'A' && nextg[i] != -1) {
			ans += tcount[nextg[i]];
		}
	}
	cout << ans << endl;
}