#include <algorithm>
#include <array>
#include <cassert>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <iostream>
#include <string>

constexpr auto nchars = ('Z' - 'A') + 1;

int nAGCT(const std::array<int, nchars> a, const int rot) {
  int res = 0;
  for (const auto n : {'A', 'G', 'C', 'T'})
    res += a[(((n - 'A' - rot) % nchars) + nchars) % nchars];
  return res;
}

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

  std::string s;
  std::cin >> s;

  assert(static_cast<int>(std::size(s)) == n);
  assert(std::all_of(s.cbegin(), s.cend(), [](const char c) { return std::isupper(c); }));

  std::array<int, nchars> cnt;
  cnt.fill(0);

  for (const char c : s)
    ++cnt[c - 'A'];

  int rot = 0, res = 0;

  __gnu_pbds::tree<int, __gnu_pbds::null_type, std::less<int>, __gnu_pbds::rb_tree_tag, __gnu_pbds::tree_order_statistics_node_update> t;
  for (int i = 0; i < n; ++i)
    t.insert(i);

  while (true) {
    int left = nAGCT(cnt, rot);

    if (left == 0) {
      std::cout << res << '\n';
      return 0;
    }

    auto iter = t.find_by_order(left - 1);
    --cnt[s[*iter] - 'A'];
    rot += cnt[s[*iter] - 'A'];
    t.erase(iter);

    ++res;
  }
}