#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define pb push_back
#define F first
#define S second
#define nl "\n"
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef pair<int,int> pii;

#define maxn 100005

string s;
int pres[maxn],prep[maxn],sufs[maxn],sufu[maxn];

void solve() {
	int n; cin >> n;
	cin>>s; int len=s.length();
	int lstp=-1,lsts=-1,ss=len,uu=len;
	for(int i=0;i<len;i++)
	{
		prep[i]=lstp; pres[i]=lsts;
		if(s[i]=='p') lstp=i;
		if(s[i]=='s') lsts=i;
	}

	for(int i=len-1;i>=0;i--)
	{
		sufs[i]=ss; sufu[i]=uu;
		if(s[i]=='s') ss=i;
		if(s[i]=='u') uu=i;
	}
	
	int ans=6*len;

	for(int i=0;i<len;i++)
	{
		if(s[i]!='b') continue;
		int p1=prep[i];
		if(p1==-1) continue;
		int p2=pres[p1];
		if(p2==-1) continue;

		int s1=sufs[i];
		if(s1==len) continue;
		int s2=sufu[s1];
		if(s2==len) continue;

		ans=min(ans,(i-p1)+(i-p2-1)+(s1-i)+(s2-i-1));
	}
	ans -= 4;

	cout<<ans<<endl;
	return;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	solve();
	return 0;
}