#include<iostream>
#include<cstring>
#include<vector>
#include<array>
using namespace std;
using LL = long long;

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    const LL INF = 1e18;
    int n;
    string s;
    cin >> n >> s;
    s = " " + s;
    vector<array<LL, 2> > pre(n + 2, array<LL, 2>{-INF, -INF}), suf(n + 2, array<LL, 2>{INF, INF});
    for(int i = 1; i <= n; i++){
        pre[i] = pre[i - 1];
        if (s[i] == 's'){
            pre[i][0] = max(pre[i][0], 1LL * i);
        }
        if (s[i] == 'p'){
            pre[i][1] = max(pre[i][1], pre[i][0] + i);
        }
    }
    for(int i = n; i >= 1; i--){
        suf[i] = suf[i + 1];
        if (s[i] == 'u'){
            suf[i][0] = min(suf[i][0], 1LL * i);
        }
        if (s[i] == 's'){
            suf[i][1] = min(suf[i][1], suf[i][0] + i);
        }
    }
    LL ans = INF;
    for(int i = 2; i <= n - 2; i++){
        if (s[i] == 'b'){
            ans = min(ans, (2 * i - 3) - pre[i - 1][1] + suf[i + 1][1] - (2 * i + 3));
        }
    }
    cout << ans << '\n';

}