#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef long double ld;
typedef pair<ld,ld> pld;

#define fi first
#define se second
#define pb push_back

#define rep(i,a,b) for (int i=int(a);i < int(b);i++)

#define ffor(i,n) for (int i=0;i <int(n);i++)  
#define sz(x) ((int) (x).size()) 
#define all(x) x.begin(),x.end()




ll nxt[100005][30];
ll pre[100005][30];


int main() {  
    ios_base::sync_with_stdio(false);  cin.tie(NULL);
  
    ll n ; cin >> n;
    string s ; cin >> s;

    for (int i = 0 ; i <= n ; i++) {
      for (int j = 0 ; j < 26 ; j++) {
        nxt[i][j] = n;
        pre[i][j] = -1;
      }
    }

    for (int i = n-1; i >= 0 ; i--) {
      for (int j = 0 ; j < 26 ; j++) {
        nxt[i][j] = nxt[i+1][j];
      }
      int id = int(s[i]-'a');
      nxt[i][id] = i;
    }

    for (int i = 0 ; i <= n-1 ; i++) {
        if (i > 0) {

            for (int j = 0 ; j < 26 ; j++) {
               pre[i][j] = pre[i-1][j];
            }

        }
    
        
        int id = int(s[i]-'a');
        pre[i][id] = i;
    }
    
    ll res = 1e18;
    for (int i = 2 ; i+2 < n ; i++) {
        if (s[i] == 'b') {
        //  cout << "AT : " << i << '\n';
            ll cost = 0;

            int id1 = int('p' - 'a');
            int id2 = int('s' - 'a');
            
            int p1 = pre[i-1][id1];
            if (p1 <= 0) continue;

           // cout << "P1 : " << p1 << '\n';
            ll len1 = i - p1 - 1; 
            cost += len1*2;
            
            int p2 = pre[p1-1][id2];
           //  cout << "P2 : " << p2 << '\n';
            if (p2 < 0) continue;
            ll len2 = p1 - p2 - 1;
            cost += len2;


            id1 = int('s' - 'a');
            id2 = int('u' - 'a');

            p1 = nxt[i+1][id1];
           // cout << "N1 : " << p1 << '\n';
            if (p1+1 >= n) continue;
             len1 = p1 - i - 1; 
            cost += len1*2;

            p2 = nxt[p1+1][id2];
          //  cout << "N2 : " << p2 << '\n';
            if (p2 >= n) continue;
             len2 = p2 - p1 - 1;
            cost += len2;


           // cout << "COST : " << cost << '\n';
            res = min(res,cost);
        }
    }
    cout << res << '\n';
    

      





  
}