#include <bits/stdc++.h>
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define st first
#define nd second
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;
const int N = 1e6 + 5;

int main() {
	ios_base::sync_with_stdio(false); cin.tie(0);
	int n; cin >> n;
	string s; cin >> s;
	vector<array<int, 26>> nxtR(n), nxtL(n);
	for (int i = n - 1; i >= 0; i--) {
		for (int j = 0; j < 26; j++)
			nxtR[i][j] = i + 1 == n ? n : nxtR[i + 1][j];
		s[i] -= 'a';
		nxtR[i][s[i]] = i;
	}
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 26; j++)
			nxtL[i][j] = i == 0 ? -1 : nxtL[i - 1][j];
		nxtL[i][s[i]] = i;
	}
	int ans = 10 * n;
	string t = "spbsu";
	for (int i = 0; i < n; i++) {
		if (s[i] != 'b' - 'a')
			continue;
		int x = i, y = i, cnt = 0;
		for (char c: {'s', 'u'}) {
			x = nxtR[x][c - 'a'];
			if (x == n)
				break;
			cnt += x - i - (c == 's' ? 1 : 2);
		}
		for (char c: {'p', 's'}) {
			y = nxtL[y][c - 'a'];
			if (y == -1)
				break;
			cnt += i - (c == 'p' ? 1 : 2) - y;
		}
		if (x < n && y >= 0)
			ans = min(ans, cnt);
	}
	cout << ans << "\n";
}