#include "bits/stdc++.h"
using namespace std;
typedef long long ll;

#define rep(i, begin, end) for(int i = begin; i < end; i++)
#define all(x) x.begin(),x.end()
#define sz(x) (int)x.size()
#define sq(x) (x)*(x)

const int N = 112345;
const int inf = 1e9+7;

void solvetask()
{
    int n;
    cin >> n;

    string s; cin >> s;
    string t = "spbsu";
    queue<int> q[5];
    
    rep(i, 0, n){
        rep(j,0,5)
            if(s[i] == t[j])
                q[j].push(i);
    }

    q[3].pop();

    int res = inf;
    int s1 = -inf;
    int p = -inf;
    while(1){
        if(q[2].empty() || q[0].empty() || q[1].empty()) break;
        while(!q[1].empty() && q[1].front() < q[2].front()){
            p = q[1].front();
            q[1].pop();
        }
        while(!q[0].empty() && q[0].front() < p){
            s1 = q[0].front();
            q[0].pop();
        }
        
        int esq = q[2].front()-2 - s1 + q[2].front()-1-p;

        while(!q[3].empty() && q[3].front() < q[2].front()){
            q[3].pop();
        }
        if(q[3].empty()) break;
        while(!q[4].empty() && q[4].front() < q[3].front()){
            q[4].pop();
        }
        if(q[4].empty()) break;

        // cout << "DIR " << q[3].front() << " " << q[4].front() << '\n';
        res = min(res, esq + q[3].front() - q[2].front() - 1 + q[4].front() - q[2].front()-2);
        q[2].pop();
    }

    cout << res << '\n';


}

int main()
{
    cin.tie(0)->sync_with_stdio(0);
    int t = 1;
    // cin >> t;
    while (t--)
        solvetask();
        // cout << (solvetask() ? "Yes" : "No") << '\n';
}