#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define eb emplace_back
//mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
#define mod 998244353
#define ll long long
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f
inline int read()
{
	char ch=getchar(); int nega=1; while(!isdigit(ch)) {if(ch=='-') nega=-1; ch=getchar();}
	int ans=0; while(isdigit(ch)) {ans=ans*10+ch-48;ch=getchar();}
	if(nega==-1) return -ans;
	return ans;
}
void print(vector<int> x){for(int i=0;i<(int)x.size();i++) printf("%d%c",x[i]," \n"[i==(int)x.size()-1]);}
#define N 100005
int f[N][6],n;
char s[N];
signed main()
{
	cin>>n; scanf("%s",s+1);
	memset(f,0x3f,sizeof(f));
	f[0][0]=0;
	for(int i=1;i<=n;i++)
	{
		memcpy(f[i],f[i-1],sizeof(f[i]));
		f[i][1]++;
		f[i][2]+=2;
		f[i][3]+=2;
		f[i][4]++;
		if(s[i]=='s') f[i][1]=min(f[i][1],f[i-1][0]);
		if(s[i]=='p') f[i][2]=min(f[i][2],f[i-1][1]);
		if(s[i]=='b') f[i][3]=min(f[i][3],f[i-1][2]);
		if(s[i]=='s') f[i][4]=min(f[i][4],f[i-1][3]);
		if(s[i]=='u') f[i][5]=min(f[i][5],f[i-1][4]);
	}
	cout<<f[n][5]<<endl;
	return 0;
}