#include <bits/stdc++.h>
using namespace std;

#define sza(x) ((int)x.size())
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define forn(i, n) for (int i = 0; i < int(n); i++)
#define fi first
#define se second

using ld = long double;
using ll = long long;
using str = string;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vll = vector<ll>;
const int MAX_N = 1e5 + 5;
const ll MOD = 1e9 + 7; // 998244353
const ll INF = 1e9;
const ld EPS = 1e-9;

#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
typedef tree<pii, null_type, less<pii>, rb_tree_tag, tree_order_statistics_node_update> ordered_multiset;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

/////////////////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////////////////

bool multiTest = 0;

void solve(int tt) {
  ll n; cin >> n;
  str s; cin >> s;
  vll sIndex, pIndex, bIndex, uIndex;
  sIndex.pb(-INF - 1);
  pIndex.pb(-INF);
  forn(i, n){
    if (s[i] == 's')
      sIndex.pb(i);
    if (s[i] == 'p')
      pIndex.pb(i);
    if (s[i] == 'b')
      bIndex.pb(i);
    if (s[i] == 'u')
      uIndex.pb(i);
  }
  uIndex.pb(INF+1);
  sIndex.pb(INF);
  ll ans = INF;
  forn(i, bIndex.size()){
    // cerr << bIndex[i] << endl;
    ll pI = *(--lower_bound(all(pIndex), bIndex[i]));
    ll sI = *(--lower_bound(all(sIndex), pI));
    ll sI2 = *(upper_bound(all(sIndex), bIndex[i]));
    ll uI = *(upper_bound(all(uIndex), sI2));
    // cerr << sI << ' ' << pI << ' ' << bIndex[i] << ' ' << sI2 << ' ' << uI << endl;
    ll bI = bIndex[i];
    ll newAns = uI + sI2 - sI - pI;
    ans = min(ans, newAns);
  }
  cout << ans - 6;
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    // cout.precision(20);

    int t = 1;
    if (multiTest)
        cin >> t;
    for (int ii = 0; ii < t; ii++)
    {
        solve(ii);
    }
}