#include<bits/stdc++.h>
#define int long long
using namespace std;
const int INF=1000000000;
int n,f[1000005][7],g[1000005][7],ans(INF);
string ss,T;
signed main() {
	cin>>n;
	cin>>ss;
	ss="1"+ss;
	T="1spbsu1";
	for(int i=0; i<=n+1; i++)
		for(int j=0; j<=6; j++) {
			f[i][j]=g[i][j]=INF;
		}
	f[0][0]=g[n+1][6]=0;
	for(int i=1; i<=n; i++) {
		for(int j=0; j<=5; j++) {
			if(ss[i]!=T[j]) {
				f[i][j]=f[i-1][j];
			} else f[i][j]=f[i-1][j-1]+i;
//			cout<<f[i][j]<<" ";
		}
//		cout<<'\n';
	}
	for(int i=n; i>=1; i--) {
		for(int j=1; j<=6; j++) {
			if(ss[i]!=T[j]) {
				g[i][j]=g[i+1][j];
			} else g[i][j]=g[i+1][j+1]+i;
//			cout<<g[i][j]<<" ";
		}
//		cout<<'\n';
	}
	for(int i=1; i<=n; i++) {
		for(int j=max(1ll,-n+5+i); j<=min(i,5ll); j++) {
			if(ss[i]==T[j]&&f[i-1][j-1]<=5*n&&g[i+1][j+1]<=5*n)
				ans=min(ans,-f[i-1][j-1]+(2ll*i-j)*(j-1ll)/2ll-(2ll*i-j+6ll)*(5ll-j)/2ll+g[i+1][j+1]);
		}
	}
	cout<<ans;
	
	return 0;
}
/*
17
saaaaaapaaaaaabsu
*/