#include <bits/stdc++.h>
#define x first
#define y second
using namespace std;
using ll=long long;
using pii=pair<int,int>;
using vi=vector<int>;
using vl=vector<ll>;
#define pb push_back
#define all(a) begin(a),end(a)

const int N=300010,MOD=1e9+7;
const char en='\n';
const ll LLINF=1ll<<60;

int n;
string s;
vi pov[N];

int pre(int i,char x)
{
	auto it=lower_bound(all(pov[x]),i);
	if (it==pov[x].begin()) return -1;
	--it;
	return *it;
}

int ne(int i,char x)
{
	auto it=lower_bound(all(pov[x]),i);
	if (it==pov[x].end()) return -1;
	return *it;
}

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin>>n>>s;
	int mi=MOD;
	for (int i=0;i<n;++i) pov[s[i]].pb(i);
	for (int i=0;i<n;++i) if (s[i]=='b')
	{
		int c=i;
		int b=pre(c,'p');
		if (b==-1) continue;
		int a=pre(b,'s');
		if (a==-1) continue;
		int d=ne(c,'s');
		if (d==-1) continue;
		int e=ne(d,'u');
		if (e==-1) continue;
		mi=min(mi,(b-a-1)+(c-b-1)*2+(d-c-1)*2+(e-d-1));
	}
	cout<<mi<<en;
}