//Make CSP great again
//Vengeance
#include <bits/stdc++.h>
#define TASK "TESTCODE"
using namespace std;
const int N = 1e5;
string s;
int dp[N + 2], n;
void read()
{
    cin >> n >> s;
    s = '?' + s;
}
void solve()
{   
    int res = 1e9;
    dp[n + 1] = 1e9;
    for (int i = n, poss = -1, posu = -1; i >= 1; -- i)
    {
        dp[i] = dp[i + 1] + 2;
        if (s[i] == 's')
        {
            poss = i;
            if (posu != -1)
            {
                dp[i] = posu - poss - 1;
            } 
        }
        if (s[i] == 'u')
        {
            posu = i;
        }
    }
    for (int i = 1, poss = -1, posp = -1, sum = 1e9; i <= n; ++ i)
    {
        if (s[i] == 's')
        {
            poss = i;
        }
        if (s[i] == 'p')
        {
            posp = i;
            if (poss != -1)
            {
                sum = posp - poss - 1;
            }
        }
        if (s[i] == 'b')
        {
            res = min(res, sum + dp[i + 1] - 2);
        }
        sum += 2;
    }
    cout << res;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        //freopen(TASK".OUT", "w", stdout);
    }
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        //cout << "Case " << __ << ": ";
        read();
        solve();
    }
}