#include <bits/stdc++.h>
using namespace std;
const char el = '\n';
typedef long long ll;
const int inf = 1e9;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << setprecision(15);
  int n;
  cin >> n;
  string s;
  cin >> s;
  vector<array<int, 26>> prev(n), next(n);
  for (int i = 0; i < n; i++) {
    if (!i)
      prev[i].fill(-1);
    else
      prev[i] = prev[i - 1];
    prev[i][s[i] - 'a'] = i;
  }
  for (int i = n - 1; i >= 0; i--) {
    if (i == n - 1)
      next[i].fill(-1);
    else
      next[i] = next[i + 1];
    next[i][s[i] - 'a'] = i;
  }
  int ans = inf;
  for (int i = 0; i < n; i++)
    if (s[i] == 'b') {
      int a, b, c = i, d, e;
      b = prev[c]['p' - 'a'];
      if (!~b) continue;
      a = prev[b]['s' - 'a'];
      if (!~a) continue;
      d = next[c]['s' - 'a'];
      if (!~d) continue;
      e = next[d]['u' - 'a'];
      if (!~e) continue;
      ans = min(ans, c - a - 2 + c - b - 1 + d - c - 1 + e - c - 2);
    }
  cout << ans << el;
  return 0;
}