#include <bits/stdc++.h>
using namespace std;
const string ok = "spbsu";
vector<int> in[26], pos[26];
int n; string s;

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    if (fopen("input.in", "r")) {
        freopen("input.in", "r", stdin);
        freopen("output.out", "w", stdout);
    }
    for (int i = 0; i < ok.size(); i++) in[ok[i]-'a'].emplace_back(i);
    cin>>n>>s;
    for (int i = 0; i < n; i++) pos[s[i]-'a'].emplace_back(i);
    int res = 1e9;
    for (int i = 0; i < n; i++)
    {
        int cur = s[i] - 'a';
        if (in[cur].size())
            for (int j: in[cur])
            {
                int jj = j;
                int ans = 0;
                bool f = 1;
                int curl = i, cnt = 0;
                while (jj > 0)
                {
                    cnt++;
                    int need = ok[jj-1] - 'a';
                    int y = lower_bound(pos[need].begin(), pos[need].end(), curl) - pos[need].begin() - 1;
                    if (y >= 0)
                    {
                        curl = pos[need][y];
                        jj--;
                        ans += (i - curl - cnt);
                    }
                    else
                    {
                        f = 0;
                        break;
                    }
                }
                if (!f) break;
                cnt = 0;
                jj = j;
                int curr = i;
                while (jj < 4)
                {
                    cnt++;
                    int need = ok[jj+1] - 'a';
                    int y = upper_bound(pos[need].begin(), pos[need].end(), curr) - pos[need].begin();
                    if (y < pos[need].size())
                    {
                        curr = pos[need][y];
                        jj++;
                        ans += (curr - i - cnt);
                    }
                    else
                    {
                        f = 0;
                        break;
                    }
                }
                if (f) res = min(res, ans);
            }
    }
    cout<<res;
}