#include<iostream>
#include<cstdio>
#define N 100000
using namespace std;
const int inf=(int)(1e9);
int read()
{
	char c=0;
	int sum=0;
	while (c<'0'||c>'9') c=getchar();
	while ('0'<=c&&c<='9') sum=sum*10+c-'0',c=getchar();
	return sum;
}
int n,ans=inf,pv[N+1][26],nt[N+1][26],lst[26];
char c[N+1];
int main()
{
	n=read();
	for (int i=1;i<=n;++i)
	{
		cin>>c[i];
		for (int j=0;j<26;++j) pv[i][j]=lst[j];
		lst[c[i]-'a']=i;
	}
	for (int i=0;i<26;++i) lst[i]=0;
	for (int i=n;i>=1;--i)
	{
		for (int j=0;j<26;++j) nt[i][j]=lst[j];
		lst[c[i]-'a']=i;
	}
	for (int i=1;i<=n;++i)
		if (c[i]=='b'&&pv[i]['p'-'a']&&pv[pv[i]['p'-'a']]['s'-'a']&&nt[i]['s'-'a']&&nt[nt[i]['s'-'a']]['u'-'a'])
			ans=min(ans,nt[i]['s'-'a']+nt[nt[i]['s'-'a']]['u'-'a']-pv[i]['p'-'a']-pv[pv[i]['p'-'a']]['s'-'a']-6);
	printf("%d\n",ans);
	return 0;
}