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

inline int read()
{
	int x=0,f=1;
	char c=getchar();
	while(c<'0' || c>'9')
	{
		if(c=='-') f=-1;
		c=getchar();
	}
	while(c>='0' && c<='9')
	{
		x=x*10+c-'0';
		c=getchar();
	}
	return x*f;
}

const int N = 1e5+5;
int n;
int a[N];
char c[N];
int lef[N][26], rig[N][26];
int pos[26];

int main()
{
	n=read();
	scanf("%s",c+1);
	for(int i=1;i<=n;i++) a[i]=c[i]-'a';
	memset(pos,0,sizeof(pos));
	for(int i=1;i<=n;i++)
	{
		for(int j=0;j<26;j++) lef[i][j]=pos[j];
		pos[a[i]]=i;
	}
	memset(pos,0,sizeof(pos));
	for(int i=n;i>=1;i--)
	{
		for(int j=0;j<26;j++) rig[i][j]=pos[j];
		pos[a[i]]=i;
	}
	int ans=1e9;
	for(int i=1;i<=n;i++)
		if(c[i]=='b')
		{
			int c3=i;
			int c2=lef[c3]['p'-'a'];
			int c1=lef[c2]['s'-'a'];
			int c4=rig[c3]['s'-'a'];
			int c5=rig[c4]['u'-'a'];
			if(!c5 || !c1) continue;
			ans=min(ans,(c2-c1-1)+(c3-c2-1)*2+(c4-c3-1)*2+(c5-c4-1));
		}
	cout<<ans<<endl;
	return 0;
}