#include"bits/stdc++.h"

using namespace std;

const int N = 1e6 + 10;

int s1[N], p[N], s2[N], u[N];

void solve() {
	int n;
	cin >> n;
	string s;
	cin >> s;
	s = ' ' + s;
	int ks1 = -1, kp = -1;
	for(int i = 1; i <= n; i++) {
		s1[i] = ks1;
		p[i] = kp;
		if(s[i] == 's') ks1 = i;
		if(s[i] == 'p') kp = i;
	}
	int ks2 = -1, ku = -1;
	for(int i = n; i >= 1; i--) {
		s2[i] = ks2;
		u[i] = ku;
		if(s[i] == 's') ks2 = i;
		if(s[i] == 'u') ku = i;
	}
	int ans = 1e9 + 10;
	for(int i = 1; i <= n; i++) {
		if(p[i] == -1 || s1[p[i]] == -1 || s2[i] == -1 || u[s2[i]] == -1) continue;
		if(s[i] == 'b') {
			ans = min(2 * (i - p[i] - 1) + (p[i] - s1[p[i]] - 1) + 2 * (s2[i] - i - 1) + (u[s2[i]] - s2[i] - 1), ans);
		}
	}
	cout << ans << "\n";
}

int main() {
 	ios::sync_with_stdio(0);
 	cin.tie(0), cout.tie(0);
 	solve();
	return 0;
}

/*
6
spbssu
*/