#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
template<class T> void check_min(T &a, const T &b){ a = (a < b) ? a : b; }
template<class T> void check_max(T &a, const T &b){ a = (a > b) ? a : b; }
#define all(x) (x).begin(), (x).end()

int main(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    int n;
    cin >> n;

    string s;
    cin >> s;

    static const int N = 1e5 + 3;
    static int dp[N][6];
    const int INF = 1e9;

    string pat = "spbsu";

    for(int i = n; i >= 0; --i){
        for(int j = 0; j <= 5; ++j){
            int &ans = dp[i][j];
            if(i == n){
                ans = (j == 5) ? 0 : INF;
                continue;
            }

            ans = dp[i + 1][j];

            if(j != 5){
                if(s[i] == pat[j]){
                    int cand = dp[i + 1][j + 1];
                    if(j <= 1)
                        cand -= i;
                    else if(j >= 3)
                        cand += i;
                    check_min(ans, cand);
                }
            }
        }
    }

    cout << dp[0][0] - 6 << "\n";
}