#include <bits/stdc++.h>
using namespace std;

using ll = long long;
//#define int ll
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
using pii = pair<int, int>;
using vi = vector<int>;
#define fi first
#define se second
#define pb push_back

const int N=1e5+100,A=26;
int prv[N][A],nxt[N][A];

signed main() {
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(cin.failbit);

    int n;
    cin>>n;
    string s;
    cin>>s;
    s="_"+s;
    for(int j=0;j<A;j++)
        nxt[n+1][j]=n+1;
    for(int i=n;i>=1;i--)
    {
        for(int j=0;j<A;j++)
            nxt[i][j]=nxt[i+1][j];
        nxt[i][s[i]-'a']=i;
    }
    for(int j=0;j<A;j++)
        prv[0][j]=0;
    for(int i=1;i<=n;i++)
    {
        for(int j=0;j<A;j++)
            prv[i][j]=prv[i-1][j];
        prv[i][s[i]-'a']=i;
    }
    int ans=1e9;
    for(int m=1;m<=n;m++)
    {
        if(s[m]!='b')
            continue;
        int i=m,res=0,j;

        j=nxt[i+1]['s'-'a'];
        if(j>n) continue;
        res+=(j-i-1)*2;
        i=j;

        j=nxt[i+1]['u'-'a'];
        if(j>n) continue;
        res+=(j-i-1)*1;

        i=m;

        j=prv[i-1]['p'-'a'];
        if(j<1) continue;
        res+=(i-j-1)*2;
        i=j;

        j=prv[i-1]['s'-'a'];
        if(j<1) continue;
        res+=(i-j-1)*1;

        ans=min(ans,res);
    }
    cout<<ans;
}