#include<algorithm>
#include<iostream>
#include<string>
#include<string.h>
#include<array>
#include<cmath>
#include<iterator>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<vector>
#include<cfloat>
#include<climits>
#include<complex>
#include<deque>
#include<fstream>
#include<functional>
#include<iomanip>
#include<list>
#include<memory>
#include<stack>
#include<random>
using namespace std;

int main() {
    int n;
    string s;
    cin >> n >> s;
    map<char,vector<int>>mp;
    for(int i = 0; i < n; i++) {
        mp[s[i]].push_back(i);
    }
    int ans = 1001001001;
    for(int i = 0; i < n; i++) {
        if(s[i] == 'b') {
            vector<int>a = mp['s'];
            vector<int>b = mp['p'];
            vector<int>c = mp['u'];
            int it1 = lower_bound(b.begin(),b.end(),i)-b.begin();
            if(it1 == 0) continue;
            it1--;
            int it2 = lower_bound(a.begin(),a.end(),b[it1])-a.begin();
            if(it2 == 0) continue;
            it2--;
            int it3 = lower_bound(a.begin(),a.end(),i)-a.begin();
            if(it3 == a.size()) continue;
            int it4 = lower_bound(c.begin(),c.end(),a[it3])-c.begin();
            if(it4 == c.size()) continue;
            int sum = 0;
            sum += i-1-b[it1];
            sum += i-2-a[it2];
            sum += a[it3]-i-1;
            sum += c[it4]-i-2;
            ans = min(ans,sum);
        }
    }
    cout << ans << "\n";
}