#include <algorithm>
#include <iostream>
#include <iterator>
#include <list>

int main() {
  int n;
  std::cin >> n;

  std::list<char> s;
  std::copy_n(std::istream_iterator<char>(std::cin), n, std::back_inserter(s));

  const auto is_AGCT = [](const char c) {
    return c == 'A' || c == 'G' || c == 'C' || c == 'T';
  };

  auto to_remove = std::count_if(s.cbegin(), s.cend(), is_AGCT);
  if (to_remove == 0) {
    std::cout << "0\n";
    return 0;
  }

  auto iter = std::next(s.begin(), to_remove - 1);
  int res   = 0;

  while (true) {
    bool f = is_AGCT(*iter);
    iter   = s.erase(iter);
    ++res;
    if (f) {
      if (to_remove == 1) {
        break;
      } else {
        --to_remove;
        --iter;
      }
    }
  }

  std::cout << res << '\n';
}