#include <bits/stdc++.h>
using namespace std;

int n, m, c;
string s;

int ct(string s) {
	int u = 0;

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

	return u;
}

int main()
{
	cin >> n >> s;

	while (c = ct(s)) {
		s = s.substr(0, c - 1) + s.substr(c, n - c);
		n--;
		m++;
	}

	cout << m << endl;
}