#include<bits/stdc++.h>
using namespace std;
template<typename T>inline void read(T &x){
    x=0;
    char ch=getchar();
    bool flag=0;
    while(ch>'9'||ch<'0') flag=flag||ch=='-',ch=getchar();
    while(ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();
    x=flag?-x:x;
}
template<typename T,typename ...Args>inline void read(T &x,Args &...args){
    read(x),read(args...);
}
template<typename T>inline void prt(T x){
    if(x>9) prt(x/10);
    putchar(x%10+'0');
}
template<typename T>inline void put(T x){
    if(x<0) putchar('-'),x=-x;
    prt(x);
}
template<typename T>inline void put(char ch,T x){
    put(x),putchar(ch);
}
template<typename T,typename ...Args>inline void put(char ch,T x,Args ...args){
    put(ch,x),put(ch,args...);
}
#define N 100005
int n;
char s[N];
int pre[N][26],suf[N][26];
inline int calc(int x,int y){
	return y-x;
}
int main(){
	read(n),scanf("%s",s+1);
	for(int i=1;i<=n;i++){
		for(int j=0;j<26;j++) pre[i][j]=pre[i-1][j];
		pre[i][s[i]-'a']=i;
	}		 
	for(int i=n;i;i--){
		for(int j=0;j<26;j++) suf[i][j]=suf[i+1][j];
		suf[i][s[i]-'a']=i;
	}
	int ans=2e9;
	for(int i=1;i<=n;i++){
		if(s[i]!='b') continue;
		int l0=pre[i]['p'-'a'],l1=pre[l0]['s'-'a'],r0=suf[i]['s'-'a'],r1=suf[r0]['u'-'a'];
		if(!l0||!l1||!r0||!r1) continue;
		ans=min(ans,calc(l0,i-2)+calc(l1,i-1)+calc(i+1,r0)+calc(i+2,r1));
	}
	put('\n',ans);
	return 0;
}