#include<bits/stdc++.h>
#define re register
using namespace std;
inline int read(){
	re int t=0;re char v=getchar();
	while(v<'0')v=getchar();
	while(v>='0')t=(t<<3)+(t<<1)+v-48,v=getchar();
	return t;
}
const int M=998244353;
inline void add(re int &x,re int y){(x+=y)>=M?x-=M:x;}
inline int Mod(re int x){return x>=M?x-M:x;}
inline int ksm(re int x,re int y){
	re int s=1;
	while(y){
		if(y&1)s=1ll*s*x%M;
		x=1ll*x*x%M,y>>=1;
	}
	return s;
}
int t,n,m,nxt[100002][26],ans,lst[100002][26];
char s[1000002];
int main(){
	n=read(),scanf("%s",s+1),ans=1e9;
	for(re int i=0;i<26;++i)nxt[n+1][i]=n+1;
	for(re int i=n;i;--i){
		for(re int j=0;j<26;++j)nxt[i][j]=nxt[i+1][j];
		nxt[i][s[i]-'a']=i;
	}
	for(re int i=1;i<=n;++i){
		for(re int j=0;j<26;++j)lst[i][j]=lst[i-1][j];
		lst[i][s[i]-'a']=i;
	}
	for(re int i=1;i<=n;++i)if(s[i]=='b'){
		deque<int>A;
		A.push_back(i);
		re int pos=i;
		pos=nxt[pos]['s'-'a'];
		if(pos==n+1)continue;
		A.push_back(pos);
		pos=nxt[pos]['u'-'a'];
		if(pos==n+1)continue;
		A.push_back(pos);
		pos=i;
		pos=lst[pos]['p'-'a'];
		if(pos==0)continue;
		A.push_front(pos);
		pos=lst[pos]['s'-'a'];
		if(pos==0)continue;
		A.push_front(pos);
		ans=min(ans,A[2]-A[1]-1+A[2]-A[0]-2+A[4]-A[2]-2+A[3]-A[2]-1);
	}
	printf("%d",ans);
}