// C++ includes used for precompiling -*- C++ -*-

// Copyright (C) 2003-2013 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file stdc++.h
 *  This is an implementation file for a precompiled header.
 */

// Also writing "using namespace std;" here so that you dont need to write it everytime you start a cpp file

using namespace std;


// 17.4.1.2 Headers

// C
#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif

#define lsb(x) (x & (-x))

using ull = unsigned long long;
using ll = long long;

using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    string f = "spbsu";
    int n;
    string s;
    cin >> n;
    cin >> s;
    vector<vector<int>> dp(n + 1, vector<int> (5, 5 * n));
    
    deque<int> v[26];
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < f.size(); ++j) {
            if (i > 0)
                dp[i][j] = dp[i - 1][j];
            if (s[i] == f[j]) {
                if (i == 0) {
                    if (j == 0)
                        dp[i][0] = -2;
                } else {
                    if (j == 0)
                        dp[i][0] = -i - 2;
                    else if (j == 1)
                        dp[i][1] = min(dp[i - 1][1], dp[i - 1][0] - i - 1);
                    else if (j == 2)
                        dp[i][2] = min(dp[i - 1][2], dp[i - 1][1]);
                    else if (j == 3)
                        dp[i][j] = min(dp[i - 1][j], dp[i - 1][j - 1] + i - 1);
                    else
                        dp[i][j] = min(dp[i - 1][j], dp[i - 1][j - 1] + i - 2);
                }
            }
           // cout << dp[i][j] << " ";
        }
        //cout << "\n";
    }

    cout << dp[n - 1][4] << "\n";
    return 0;
}