/*
 * author:  ADMathNoob
 * created: 09/09/23 13:59:15
 * problem: https://qoj.ac/problem/7175
 */

/*
Comments about problem:


*/

#include <bits/stdc++.h>

using namespace std;

#ifdef _DEBUG
#include "debug.h"
#else
#define debug(...) 42
#endif

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  string s;
  cin >> s;
  const int inf = 5 * n;

  auto Get = [&](string s, string t) {
    const int m = t.size();
    vector<vector<int>> dp(n, vector<int>(m, inf));
    for (int i = 0; i < n; i++) {
      if (i > 0) {
        for (int j = 0; j < m; j++) {
          dp[i][j] = dp[i - 1][j] + (j + 1);
        }
      }
      for (int j = 0; j < m; j++) {
        if (s[i] == t[j]) {
          if (j == 0) {
            dp[i][0] = 0;
          } else {
            if (i > 0) {
              dp[i][j] = min(dp[i][j], dp[i - 1][j - 1]);
            }
          }
        }
      }
    }
    return dp;
  };

  auto dp1 = Get(s, "spb");
  string rev = s;
  reverse(rev.begin(), rev.end());
  auto dp2 = Get(rev, "us");
  reverse(dp2.begin(), dp2.end());
  int ans = inf;
  for (int i = 2; i + 2 < n; i++) {
    ans = min(ans, dp1[i][2] + dp2[i + 1][1]);
  }
  cout << ans << '\n';
  return 0;
}