#include <iostream>
#include <string>
using namespace std;
int main(void){
    int n;
    cin >> n;
    string s, agct = "AGCT";
    cin >> s;
    int c = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < 4; j++) {
            if (s[i] == agct[j]) {
                c++;
                break;
            }
        }
    }
    
    int cnt = 0;
    bool b;
    while (c != 0) {
        b = false;
        for (int j = 0; j < 4; j++) {
            if (s[c-1] == agct[j]) {
                s.erase(c-1, 1);
                b = true;
                c--;
                break;
            }
        }
        if (b == false) s.erase(c-1, 1);
        cnt++;
    }
    cout << cnt << endl;
}