#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;

	while (1) {
		cnt = 0;
		for (int i = 0; i < n; i++) {
			if (s[i] == 'A' || s[i] == 'G' || s[i] == 'C' || s[i] == 'T') {
				cnt++;
			}
		}
		if (cnt == 0) {
			break;
		}
		s.erase(s.begin() + cnt - 1);
		ans++;
		n = n - 1;
	}

	cout << ans << endl;

	return 0;

}