#include <bits/stdc++.h>
using namespace std;

#define int long long

signed main() {
	ios::sync_with_stdio(0); cin.tie(0);
	
	int n; cin >> n;
	string s; cin >> s;

	vector<int> fr(n, -998244353), ba(n, 998244353);
	int lss = -998244353;
	for (int i = 0; i < n; i++) {
		if (s[i] == 's') lss = i;
		else if (s[i] == 'p') fr[i] = lss;
	}
	lss = 998244353;
	for (int i = n-1; i >= 0; i--) {
		if (s[i] == 'u') lss = i;
		else if (s[i] == 's') ba[i] = lss;
	}

	vector<int> l(n, 998244353), r(n, 998244353);
	int cst = 998244353;
	for (int i = 0; i < n; i++) {
		if (s[i] == 'b') {
			l[i] = cst;
		} else if (s[i] == 'p') {
			cst = min(cst, abs(i - fr[i]));
		}
		cst += 2;
	}
	cst = 998244353;
	for (int i = n-1; i >= 0; i--) {
		if (s[i] == 'b') {
			r[i] = cst;
		} else if (s[i] == 's') {
			cst = min(cst, abs(i - ba[i]));
		}
		cst += 2;
	}

	int ans = 998244353;
	for (int i = 0; i < n; i++) {
		if (s[i] == 'b') {
			ans = min(ans, l[i] + r[i]);
		}
	}
	cout << ans-6 << '\n';

	return 0;
}