// g++-13 1.cpp -std=c++17 -O2 -I .
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;
 
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vld = vector<ld>;
using vvld = vector<vld>;
using vst = vector<string>;
using vvst = vector<vst>;
 
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define pq_big(T) priority_queue<T,vector<T>,less<T>>
#define pq_small(T) priority_queue<T,vector<T>,greater<T>>
#define all(a) a.begin(),a.end()
#define rep(i,start,end) for(ll i=start;i<(ll)(end);i++)
#define per(i,start,end) for(ll i=start;i>=(ll)(end);i--)
#define uniq(a) sort(all(a));a.erase(unique(all(a)),a.end())

string init = "spbsu";

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

  int n;cin>>n;
  string s;cin>>s;

  vvi index(26);
  rep(i,0,n){
    index[s[i]-'a'].emplace_back(i);
  }
  rep(i,0,26){
    index[i].emplace_back(2*n+10);
  }

  int ans=1e7;
  rep(i,0,n){
    
    rep(j,0,5){
      if(s[i]==init[j]){
        int now=0;
        int ind=i;
        per(k,j-1,0){
          if(i-j+k<0){
            now=1e8;
            break;
          }
          auto it=lower_bound(all(index[init[k]-'a']),ind);
          if(it-index[init[k]-'a'].begin()==0){
            now=1e8;
            break;
          }
          it--;
          now+=abs(*it-(i-j+k));
          ind=*it;
        }
        ind=i;
        rep(k,j+1,5){
          if(n<=i-j+k){
            now=1e8;
            break;
          }
          auto it=lower_bound(all(index[init[k]-'a']),ind+1);
          if(*it==2*n+10){
            now=1e8;
            break;
          }
          now+=abs(*it-(i-j+k));
          ind=*it;
        }

        //cout<<i<<" "<<j<<" "<<now<<endl;
        ans=min(ans,now);
      }
    }
  }

  cout<<ans<<endl;
}