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

int n, m, c;
string s;
bool f;

bool ist(string s, int t) {
	return s[t] == 'A' || s[t] == 'G' || s[t] == 'C' || s[t] == 'T';
}

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

	for (int i = 0; i < s.size(); i++) {
		if(ist(s, i))
			c++;
	}

	while (c) {
		f = ist(s, c - 1);
		s = s.substr(0, c - 1) + s.substr(c, n - c);

		if (f)
			c--;

		n--;
		m++;
	}

	cout << m << endl;
}