#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <set>
#include <map>
#include <queue>
using namespace std;
int main()
{
    int N;
    cin >> N;
    string S;
    cin >> S;
    int cnt = 0;
    set<char> s;
    s.insert('A');
    s.insert('C');
    s.insert('G');
    s.insert('T');
    for (int i = 0; i < N; i++)
    {
        if (S[i] == 'A' || S[i] == 'C' || S[i] == 'G' || S[i] == 'T')
            cnt++;
    }
    int ans = 0;
    int ind = cnt - 2;
    int rest = cnt;
    while (rest > 0)
    {
        bool f = false;
        for (int i = cnt - 1; i < N; i++)
        {
            f = true;
            ans++;
            if (s.count(S[i]))
            {
                cnt = i + 2;
                rest--;
                while (ind >= 0)
                {
                    if (s.count(S[ind]))
                    {
                        ans++;
                        rest--;
                        ind--;
                    }
                    else
                    {
                        ans++;
                        ind--;
                        break;
                    }
                }
                break;
            }
        }
        if (!f)
        {
            while (ind >= 0 && rest > 0)
            {
                if (s.count(S[ind]))
                {
                    rest--;
                }
                ind--;
                ans++;
            }
        }
    }
    cout << ans << endl;
}