//
// Created by lv_shen on 2023/9/9.
//

#include <bits/stdc++.h>

#define endl "\n"
using namespace std;
typedef long long LL;
typedef unsigned long long u64;
typedef pair<int, int> PII;
const int N = 2e5 + 10;
const int mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;

int main () {
	std::ios::sync_with_stdio (false);
	std::cin.tie (nullptr);
	std::cout.tie (nullptr);
	int n;
	string s;
	vector<int> ps, pp, pb, pu;
	cin >> n;
	cin >> s;
	for (int i = 0; i < n; i++) {
		if (s[i] == 's') ps.push_back (i);
		else if (s[i] == 'p') pp.push_back (i);
		else if (s[i] == 'b') pb.push_back (i);
		else if (s[i] == 'u') pu.push_back (i);
	}
	int ans = 1e9;
	for (int i = 0; i < pb.size (); i++) {
		int ip = upper_bound (pp.begin (), pp.end (), pb[i]) - pp.begin () - 1;
		int ifs = upper_bound (ps.begin (), ps.end (), pp[ip]) - ps.begin () - 1;
		int ies = upper_bound (ps.begin (), ps.end (), pb[i]) - ps.begin ();
		int iu = upper_bound (pu.begin (), pu.end (), ps[ies]) - pu.begin ();
		if (pp[ip] < pb[i] && ps[ifs] < pp[ip] && ies != ps.size () && iu != pu.size ()) {
			int tmp = pb[i] - ps[ifs] + pb[i] - pp[ip] + ps[ies] - pb[i] + pu[iu] - pb[i] - 6;
			ans = min (ans, tmp);
		}
	}
	cout << ans << endl;

	return 0;
}