#include<bits/stdc++.h>
using namespace std;
int n,dp[2][100010],fdp[2][100010],res;
char ch[100010];
int main(){
	//freopen("A.in","r",stdin);
	scanf("%d",&n);
	scanf("%s",ch+1);
	dp[0][0]=-2000000;
	dp[1][0]=-2000000;
	for (int i=1;i<=n;i++){
		if (ch[i]=='s') dp[0][i]=i;
		else dp[0][i]=dp[0][i-1];
		if (ch[i]=='p') dp[1][i]=i+dp[0][i];
		else dp[1][i]=dp[1][i-1];
	}
	fdp[0][n+1]=2000000;
	fdp[1][n+1]=2000000;
	for (int i=n;i;i--){
		if (ch[i]=='u') fdp[0][i]=i;
		else fdp[0][i]=fdp[0][i+1];
		if (ch[i]=='s') fdp[1][i]=i+fdp[0][i];
		else fdp[1][i]=fdp[1][i+1];
	}
	res=2000000;
	for (int i=1;i<=n;i++)
	if (ch[i]=='b'){
		res=min(res,fdp[1][i]-dp[1][i]);
		//printf("%d %d\n",fdp[1][i],dp[1][i]);
	}
	printf("%d\n",res-6);
}