#include<bits/stdc++.h>

using namespace std;
int d[100005][6][2];
string tar = "spbsu";
main() {
    int n;
    string s;
    cin >> n >> s;
    set<int> sSet, pSet, uSet;
    for (int i = 0; i < n; i ++) {
        if (s[i] == 's') {
            sSet.insert(i);
        }
        if (s[i] == 'p') {
            pSet.insert(i);
        }
        if (s[i] == 'u') {
            uSet.insert(i);
        }
    }
    int ans = 600000;
    for (int i = 0; i < n; i++) {
        int ok = 1, dist = 0;
        set<int>::iterator pLow = pSet.lower_bound(i);
        if (s[i] == 'b') {
            if (pLow == pSet.begin()) {
                ok = 0;
            } else {
                pLow --;
                dist += i - *pLow - 1;
            }
            set<int>::iterator sLow = sSet.lower_bound(i);

            if (sLow == sSet.begin()) {
                ok = 0;
            } else {
                sLow --;
                while (*sLow > *pLow) {
                    if (sLow == sSet.begin()) {
                        ok = 0;
                        break;
                    }else {
                        sLow --;
                    }
                }
                dist += i - *sLow - 2;
            }//cout << dist << "! ";



            set<int>::iterator sHi = sSet.lower_bound(i);
            if (sHi == sSet.end()) {
                ok = 0;
            } else {
                dist += *sHi - i - 1;
            }

            set<int>::iterator uHi = uSet.lower_bound(i);
            if (uHi == uSet.end()) {
                ok = 0;
            } else {
                while (*uHi < *sHi) {
                    uHi ++;
                    if (uHi == uSet.end()) {
                        ok = 0;
                        break;
                    }
                }
                dist += *uHi - i - 2;
            }
            if (ok) {
                ans = min(ans, dist);
            }
        }
    }
    cout << ans;
}