#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;

int N, cnt = 0, ans = 0;
string S;
vector<char> vec;

int main() {
  cin >> N >> S;
  for (int i = 0; i < N; i++) {
    if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T') cnt++;
    vec.push_back(S[i]);
  }
  while (cnt > 0) {
    ans++;
    char c = *(vec.begin() + cnt - 1);
    vec.erase(vec.begin() + cnt - 1);
    if (c == 'A' || c == 'G' || c == 'C' || c == 'T') cnt--;
  }
  cout << ans << endl;
  return 0;
}