#include<bits/stdc++.h>

using namespace std;
typedef long long ll;
const int N=100010;
ll qs[N],qp[N],hs[N],hu[N];
void solve()
{
	ll n;cin>>n;
	string s;cin>>s;s="1"+s;
	ll sd,pd;
	sd=-1,pd=-1;
	for (int i=1;i<s.size();i++)
	{
		qs[i]=sd;qp[i]=pd;
		if (s[i]=='s') sd=0;if (s[i]=='p') pd=0;
		if (sd>=0) sd++;if (pd>=0) pd++;
	}
	ll ud;
	sd=-1;ud=-1;
	for (int i=s.size()-1;i>=1;i--)
	{
		hs[i]=sd;hu[i]=ud;
		if (s[i]=='s') sd=0;if (s[i]=='u') ud=0;
		if (sd>=0) sd++;if (ud>=0) ud++;
	}
	ll ans=LLONG_MAX;
//	for (int i=1;i<s.size();i++)
//	{
//		cout<<qs[i]<<" "<<qp[i]<<" "<<hs[i]<<" "<<hu[i]<<"++++++++++++++++++++\n";
//	}
	for (int i=1;i<s.size();i++)
	{
		if (s[i]=='b'&&qp[i]>0&&qs[i-qp[i]]>0&&hs[i]>0&&hu[i+hs[i]]>0)
		{
			ans=min(ans,qp[i]-1+qp[i]-1+qs[i-qp[i]]-1+hs[i]-1+hs[i]-1+hu[i+hs[i]]-1);
//			cout<<qp[i]-1<<" "<<qs[i-qp[i]]-1<<" "<<hs[i]-1<<" "<<hu[i+hs[i]]-1<<"--------\n";
		}
	}
	cout<<ans;
}
int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	ll T=1;
	while(T--)
	{
		solve();
	}
	return 0;
}