// UUID: e0b39dd4-ec0e-44eb-9a3d-1633e914cb6a
#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
	int n; cin >> n;
    string s; cin >> s;

    vector<int> nextg(n+1, -1), t(n+1, 0);

    int lastg = -1;
    for(int i = n - 1; i >= 0; i--){
        if(s[i]=='G'){ 
            lastg = i;
        }
        nextg[i] = lastg;
    }

    t[n] = 0;
    for(int i = n - 1; i >= 0; i--){
        t[i] = t[i + 1] + (s[i]=='T');
    }

    ll ans = 0;
    for(int i = 0; i < n; i++){
        if(s[i]=='A'){
            int g = nextg[i + 1];
            if(g != -1){
                ans += t[g + 1];
            }
        }
    }
    cout << ans;
}