#if __INCLUDE_LEVEL__ == 0

#include <bits/stdc++.h>

using namespace std;

#include __BASE_FILE__

namespace {

void solve() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  vector<array<int, 26>> nxt(n + 1);
  nxt[n].fill(n);
  for (int i : per(n)) {
    nxt[i] = nxt[i + 1];
    nxt[i][s[i] - 'a'] = i;
  }
  vector<array<int, 26>> prv(n + 1);
  prv[0].fill(-1);
  for (int i : rep(n)) {
    prv[i + 1] = prv[i];
    prv[i + 1][s[i] - 'a'] = i;
  }
  int ans = 1e9;
  for (int i : rep(n)) {
    if (s[i] != 'b') {
      continue;
    }
    int cur = [&]() -> int {
      int ni = nxt[i + 1]['s' - 'a'];
      if (ni == n) {
        return 1e9;
      }
      int nni = nxt[ni + 1]['u' - 'a'];
      if (nni == n) {
        return 1e9;
      }
      int pi = prv[i]['p' - 'a'];
      if (pi == -1) {
        return 1e9;
      }
      int ppi = prv[pi]['s' - 'a'];
      if (ppi == -1) {
        return 1e9;
      }
      return (i - ppi - 2) + (i - pi - 1) + (ni - i - 1) + (nni - i - 2);
    }();
    chmin(ans, cur);
  }
  print(ans);
}

}  // namespace

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  solve();
}

#else  // __INCLUDE_LEVEL__

template <class T, class U = T>
bool chmin(T& x, U&& y) {
  return y < x && (x = forward<U>(y), true);
}

template <class T, class U = T>
bool chmax(T& x, U&& y) {
  return x < y && (x = forward<U>(y), true);
}

namespace std {

template <class T1, class T2>
istream& operator>>(istream& is, pair<T1, T2>& p) {
  return is >> p.first >> p.second;
}

template <class... Ts>
istream& operator>>(istream& is, tuple<Ts...>& t) {
  return apply([&is](auto&... xs) -> istream& { return (is >> ... >> xs); }, t);
}

template <class... Ts>
istream& operator>>(istream& is, tuple<Ts&...>&& t) {
  return is >> t;
}

template <class R, enable_if_t<!is_convertible_v<R, string>>* = nullptr>
auto operator>>(istream& is, R&& r) -> decltype(is >> *begin(r)) {
  for (auto&& e : r) {
    is >> e;
  }
  return is;
}

template <class T1, class T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& p) {
  return os << p.first << ' ' << p.second;
}

template <class... Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
  auto f = [&os](const auto&... xs) -> ostream& {
    [[maybe_unused]] auto sep = "";
    ((os << exchange(sep, " ") << xs), ...);
    return os;
  };
  return apply(f, t);
}

template <class R, enable_if_t<!is_convertible_v<R, string_view>>* = nullptr>
auto operator<<(ostream& os, R&& r) -> decltype(os << *begin(r)) {
  auto sep = "";
  for (auto&& e : r) {
    os << exchange(sep, " ") << e;
  }
  return os;
}

}  // namespace std

template <class... Ts>
void print(Ts&&... xs) {
  cout << tie(xs...) << '\n';
}

inline auto rep(int l, int r) { return views::iota(min(l, r), r); }
inline auto rep(int n) { return rep(0, n); }
inline auto rep1(int l, int r) { return rep(l, r + 1); }
inline auto rep1(int n) { return rep(1, n + 1); }
inline auto per(int l, int r) { return rep(l, r) | views::reverse; }
inline auto per(int n) { return per(0, n); }
inline auto per1(int l, int r) { return per(l, r + 1); }
inline auto per1(int n) { return per(1, n + 1); }

#endif  // __INCLUDE_LEVEL__