#include<bits/stdc++.h>
using namespace std;
int main()
{
	ios_base::sync_with_stdio(false);
	int n;
	cin>>n;
	string s;
	cin>>s;
	s=' '+s;
	vector<vector<int>> pre(n+5,vector<int>(26)),nxt(n+5,vector<int>(26,n+1));
	for(int i=1;i<=n;i++)
	{
		for(char ch='a';ch<='z';ch++)
		{
			pre[i][ch-'a']=pre[i-1][ch-'a'];
		}
		pre[i][s[i]-'a']=i;
	}
	for(int i=n;i>=1;i--)
	{
		for(char ch='a';ch<='z';ch++)
			nxt[i][ch-'a']=nxt[i+1][ch-'a'];
		nxt[i][s[i]-'a']=i;
	}
//	for(int i=1;i<=n;i++)cerr<<i<<' '<<pre[i]['s'-'a']<<endl;
	int ans=1e9;
	for(int i=3;i<=n-2;i++)
	{
		if(s[i]!='b')continue;
		int p1=pre[i]['p'-'a'];
		int p2=pre[p1]['s'-'a'];
		int n1=nxt[i]['s'-'a'];
		int n2=nxt[n1]['u'-'a'];
		if(p2!=0 and n2!=n+1)
			ans=min(ans,(i-p1-1)+(i-p2-2)+(n1-i-1)+(n2-i-2));
	}
	cout<<ans<<endl;
	return 0;
}