#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rp(i,a,b)        for(int i=a;i<b;i++)

void solvetask(){
    int n;
    string a;
    cin >> n >> a;
    int s = -1, p = -1, ns=-1;
    vector<int> ss, uu;

    for (int i = n-1; i > -1; i--){
        if(a[i] == 's') ss.push_back(i);
        if(a[i] == 'u') uu.push_back(i);
    }
    ll resp = 1e9;
    rp(i, 0, n){
        while(ss.size() && i >= ss.back()) ss.pop_back();
        while(uu.size() && ss.back() > uu.back()) uu.pop_back();
        if(a[i] == 'b' && s != -1 && p != -1 && ss.size() && uu.size()) resp = min(resp, {((i-2) - s) + ((i-1) - p) + (ss.back()-(i+1)) + (uu.back()-(i+2))});
        if(a[i] == 'p'){
            p = i;
            if(ns != -1){
                s = ns;
                ns = -1;
            }
        }
        if(a[i] == 's') ns = i;
    }
    cout << resp << "\n";
}

int main(){
    cin.tie(0)->sync_with_stdio(0);
    ll t = 1;
    while(t--) solvetask();
}