#include <bits/stdc++.h>

#define rep(i,s,n) for(int i = int(s); i < int(n); i++)
#define rrep(i,s,n) for(int i = int(n) - 1; i >= int(s); i--)
#define all(v) (v).begin(), (v).end()

using ll = long long;
using ull = unsigned long long;
using ld = long double;

template<class T>
bool chmin(T &a, T b) {
    if(a <= b) return false;
    a = b;
    return true;
}

template<class T>
bool chmax(T &a, T b) {
    if(a >= b) return false;
    a = b;
    return true;
}

using namespace std;

int main() {
    int n; cin >> n;
    string s; cin >> s;
    vector<int> idx(26,n);
    vector<vector<int>> nxt(n+1);
    nxt[n] = idx;
    for (int i = n-1; i >= 0; i--){
        nxt[i] = idx;
        idx[s[i]-'a'] = i;
    }
    vector<int> jdx(26,0);
    vector<vector<int>> mxt(n+1);
    mxt[0] = jdx;
    for (int i = 0; i < n; i++){
        mxt[i+1] = jdx;
        jdx[s[i]-'a'] = i;
    }
    int ans = 1e9;
    rep(i,0,n){
        if (s[i] != 'b') continue;
        int pi = mxt[i+1]['p'-'a'];
        int li = mxt[pi+1]['s'-'a'];
        int ri = nxt[i]['s'-'a'];
        int ui = nxt[ri]['u'-'a'];
        if (pi == 0 || ui == n) continue;
        int cur = (pi-li-1) + (i-pi-1)*2 + (ri-i-1)*2 + (ui-ri-1);
        chmin(ans,cur); 
    }
    cout << ans << endl;
}