#include <bits/stdc++.h>

using namespace std;
#define int long long
using pii = pair <int, int>;
#define ff first
#define ss second
#define sz(x) ((int) (x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

template <typename T1, typename T2>
void mxr(T1& a, const T2& b) {
    if (b > a) {
        a = b;
    }
}

template <typename T1, typename T2>
void mnr(T1& a, const T2& b) {
    if (b < a) {
        a = b;
    }
}

signed main() {
    ios_base::sync_with_stdio(false);
#ifdef BUY
    freopen("inputik.txt", "r", stdin);
    freopen("outputik.txt", "w", stdout);
#else
    cin.tie(nullptr);
#endif
    int n;
    cin >> n;
    string s;
    cin >> s;
    vector <vector <int> > pos(26);
    for (int i = 0; i < n; ++i) {
        pos[s[i] - 'a'].push_back(i);
    }
    vector <int> t;
    t.push_back('s' - 'a');
    t.push_back('p' - 'a');
    t.push_back('b' - 'a');
    t.push_back('s' - 'a');
    t.push_back('u' - 'a');
    int ans = INT_MAX;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < sz(t); ++j) {
            int posl = i;
            int res = 0;
            bool flag = true;
            int dst = 0;
            for (int k = j; k >= 0; --k, ++dst) {
                auto it = upper_bound(all(pos[t[k]]), posl);
                if (it == pos[t[k]].begin()) {
                    flag = false;
                    break;
                }
                --it;
                res += (i - dst) - *it;
                posl = *it;
            }
            if (!flag) {
                continue;
            }
            int posr = i + 1;
            dst = 1;
            for (int k = j + 1; k < sz(t); ++k, ++dst) {
                auto it = lower_bound(all(pos[t[k]]), posr);
                if (it == pos[t[k]].end()) {
                    flag = false;
                    break;
                }
                res += *it - (i + dst);
                posr = *it;
            }
            if (flag) {
                mnr(ans, res);
            }
        }
    }
    cout << ans;
}