#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <typename Abelian>
struct FenwickTree {
  explicit FenwickTree(const int n, const Abelian ID = 0)
      : n(n), ID(ID), data(n, ID) {}

  void add(int idx, const Abelian val) {
    for (; idx < n; idx |= idx + 1) {
      data[idx] += val;
    }
  }

  Abelian sum(int idx) const {
    Abelian res = ID;
    for (--idx; idx >= 0; idx = (idx & (idx + 1)) - 1) {
      res += data[idx];
    }
    return res;
  }

  Abelian sum(const int left, const int right) const {
    return left < right ? sum(right) - sum(left) : ID;
  }

  Abelian operator[](const int idx) const { return sum(idx, idx + 1); }

  int lower_bound(Abelian val) const {
    if (val <= ID) return 0;
    int res = 0, exponent = 1;
    while (exponent <= n) exponent <<= 1;
    for (int mask = exponent >> 1; mask > 0; mask >>= 1) {
      const int idx = res + mask - 1;
      if (idx < n && data[idx] < val) {
        val -= data[idx];
        res += mask;
      }
    }
    return res;
  }

 private:
  const int n;
  const Abelian ID;
  std::vector<Abelian> data;
};

int main() {
  constexpr int C = 26;
  const vector<int> agct{'A' - 'A', 'G' - 'A', 'C' - 'A', 'T' - 'A'};
  int n; string s; cin >> n >> s;
  int num[C]{};
  REP(i, n) ++num[s[i] - 'A'];
  FenwickTree<int> bit(n);
  REP(i, n) bit.add(i, 1);
  int ans = 0, shift = 0;
  while (true) {
    int c1 = 0;
    for (char c : agct) c1 += num[(c - shift + C) % C];
    if (c1 == 0) break;
    ++ans;
    const int idx = bit.lower_bound(c1);
    bit.add(idx, -1);
    --num[s[idx] - 'A'];
    const int c2 = num[s[idx] - 'A'];
    shift = (shift + c2) % C;
  }
  cout << ans << '\n';
  return 0;
}