#include <iostream>		//cin, cout
#include <vector>		//vector
#include <algorithm>	//sort,min,max,count
#include <string>		//string,getline, to_string
#include <cstdlib>		//abs(int)
#include <utility>		//swap, pair
#include <deque>		//deque
#include <climits>		//INT_MAX
#include <bitset>		//bitset

using namespace std;

int main() {

	int n;
	string s;
	cin >> n >> s;

	int cnt = 0;
	int ans = 0;

	cnt = 0;
	for (int i = 0; i < n; i++) {
		if (s[i] == 'A' || s[i] == 'G' || s[i] == 'C' || s[i] == 'T') {
			cnt++;
		}
	}

	while (cnt != 0) {

		int idx = -1;
		for (int i = 0; i < cnt; i++) {
			idx++;
			if (s[idx] == '0') {
				i--;
			}
		}

		if (s[idx] == 'A' || s[idx] == 'G' || s[idx] == 'C' || s[idx] == 'T') {
			cnt--;
		}
		s[idx] = '0';
		ans++;
	}

	cout << ans << endl;

	return 0;

}