#include <bits/stdc++.h>
#define de(a) cout << #a << " = " << a << "\n";
#define deg(a) cout << #a << " = " << a << " ";
#define int long long
#define sz(a) ((int)a.size())
#define all(a) a.begin(), a.end()
#define PII pair<int, int>
using LL = long long;
using namespace std;
constexpr int inf = 1e18;
constexpr int N = 1e6 + 10;
int n, m, k;
int a[N];

void solve(int Case) {
	cin >> n;
	string s; cin >> s;
	s = " " + s;
	vector ne1(n + 1, vector<int>(26)), ne2(n + 1, vector<int>(26));
	for (int i = 0; i < 26; i++) ne1[n][i] = ne2[1][i] = inf;
	for (int i = n - 1; i >= 0; i--) {
        ne1[i] = ne1[i + 1];
        ne1[i][s[i + 1] - 'a'] = i + 1;
    }
	for (int i = 2; i <= n; i++) {
        ne2[i] = ne2[i - 1];
        ne2[i][s[i - 1] - 'a'] = i - 1;
    }

    int ans = inf;
    int mid = (n - 1) / 2 + 1;
    for (int i = 1; i <= n; i++) {
    	if (s[i] == 'b') {
    		int p[5];
    		p[2] = i;
    		p[1] = ne2[p[2]]['p' - 'a'];
    		if (p[1] > inf - 10000) continue;
    		p[0] = ne2[p[1]]['s' - 'a'];
    		if (p[2] > inf - 10000) continue;
    		p[3] = ne1[p[2]]['s' - 'a'];
    		if (p[3] > inf - 10000) continue;
    		p[4] = ne1[p[3]]['u' - 'a'];
    		if (p[4] > inf - 10000) continue;

    		auto ds = [](int a, int b) {
    			return abs(a - b) - 1;
    		};
    		int res = ds(p[1], p[0]) + 2 * ds(p[2], p[1]) + 2 * ds(p[3], p[2]) + ds(p[4], p[3]);
    		ans = min(ans, res);
    	}
    }
    cout << ans;
}

signed main() {
	cin.tie(0)->ios::sync_with_stdio(false);

	int T = 1;
	// cin >> T; cin.get();

	int Case = 0;
	while (++Case <= T) {
		solve(Case);;
	}

	return 0;
}