#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <string>
#include <list>
#include <cassert>
#include <numeric>
#include <cstdint>
#include <queue>
#include <deque>
#include <stack>
#include <set>
#include <random>
#include <bitset>
// #include <atcoder/all>
 
using ll = long long;
using ld = long double;
using namespace std;
// using namespace atcoder;
using P = pair<ll, ll>;
using Graph = vector<vector<int>>;
using Priority = priority_queue<ll, vector<ll>, greater<ll>>;// 昇順
using Priority_pair = priority_queue<P, vector<P>, greater<P>>;
// using mint_17 = modint1000000007;
// using mint = modint998244353;

#define mod 1000000007
#define MAX_WIDTH 60
#define MAX_HEIGHT 60
#define INF 1e18
#define MOD 998244353
#define PI 3.141592653589793
#define rep(i, a, b) for(ll i=(a);i<(b);i++)
#define rrep(i, a, b) for(ll i=(a);i>=(b);i--)
#define fore(i, a) for(auto &i: a)
#define all(v) (v).begin(), (v).end()
#define YES(a) cout << ((a) ? "YES" : "NO") << endl
#define Yes(a) cout << ((a) ? "Yes" : "No") << endl
#define pb(a) push_back(a)
#define vi vector<int>
#define vll vector<ll>
#define vs vector<string>
#define vc vector<char>
#define vp vector<pair<ll, ll>>
#define mll map<ll, ll>
#define msl map<string, ll>
#define COUT(n) cout << (n) << endl
#define isInGrid(n, h, w) (0 <= (n) && (n) < (h) && 0 <= (n) && (n) < (w))
template<typename T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<typename T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
int vx[] = {1,0,-1,0}, vy[] = {0,1,0,-1};

ll N;
string S;
int main() {
    cin >> N >> S;

    ll C = 0;
    set<ll> s;
    rep(i, 0, N) {
        if(S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T') {
            C++;
            s.insert(i);
        }
    }

    ll ans = 0, d = 0;
    C--;
    while(C >= 0) {
        auto ite = s.lower_bound(C);
        ll len = (*ite)-C+1;
        if(*ite != C) len -= d;
        d += len;
        ans += len;
        s.erase(ite);
        C--;
    }
    COUT(ans);

    return 0;
}