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

#define rep(i,f,t) for (int i = f; i < t; i++)
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define trav(a,x) for (auto& a : x)
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef long long ll;

int main() {
	cin.tie(0)->sync_with_stdio(0);
	int N;
	cin >> N;
	string str;
	cin >> str;
	int spos = -1, ppos = -1, upos = -1;
	vi lspos(N);
	vi lppos(N);
	vi lupos(N);
	rep(i,0,N) {
		if (str[i] == 's') spos = i;
		if (str[i] == 'p') ppos = i;
		if (str[i] == 'u') upos = i;
		lspos[i] = spos;
		lppos[i] = ppos;
		lupos[i] = upos;
	}
	vi lspos2(N);
	vi lppos2(N);
	vi lupos2(N);
	spos = -1, ppos = -1, upos = -1;
	for (int i = N-1; i >= 0; i--) {
		if (str[i] == 's') spos = i;
		if (str[i] == 'p') ppos = i;
		if (str[i] == 'u') upos = i;
		lspos2[i] = spos;
		lppos2[i] = ppos;
		lupos2[i] = upos;
	}
	int best = INT_MAX;
	rep(i,0,N) {
		if (str[i] == 'b') {
			int s = lspos2[i];
			if (s == -1) { continue; }
			int u = lupos2[s];
			if (u == -1) { continue; }
			int r = 0;
			r += s - (i+1);
			r += u - (i+2);
			int p = lppos[i];
			if (p == -1) { continue; }
			s = lspos[p];
			if (s == -1) { continue; }
			r += (i-1) - p;
			r += (i-2) - s;
			best = min(best, r);
		}
	}
	cout << best << endl;
}