#include <bits/stdc++.h>
using namespace std;
const int maxn=1e5+5;
int c1[maxn],c2[maxn],c3[maxn],c4[maxn],c5[maxn],c6[maxn];
int main()
{
  //freopen("1.in","r",stdin);
  //freopen("1.out","w",stdout);
  int n;
  cin>>n;
  string ss;
  cin>>ss;
  ss=" "+ss;
  for(int i=1;i<=n;i++)
  {
    if(ss[i]=='p')
      c2[i]=i;
    else
      c2[i]=c2[i-1];
    if(ss[i]=='s')
      c1[i]=i;
    else
      c1[i]=c1[i-1];
    if(c1[i]<c2[i])
      c3[i]=c1[i];
    else 
      c3[i]=c3[i-1];
  }
  for(int i=n;i>=1;i--)
  {
    if(ss[i]=='s')
      c5[i]=i;
    else
      c5[i]=c5[i+1];
    if(ss[i]=='u')
      c6[i]=i;
    else
      c6[i]=c6[i+1];
    if(c5[i]<c6[i])
      c4[i]=c6[i];
    else
      c4[i]=c4[i+1];
  }
  int ans=1e9;
  for(int i=1;i<=n;i++)
  {
    if(ss[i]=='b')
    {
      if(c3[i]==0||c4[i]==0||c5[i]==0||c2[i]==0)
        continue;
      ans=min(ans,(i-c2[i]-2)+(i-c3[i]-1)+(c4[i]-i-2)+c5[i]-i-1);
    }
  }
  cout<<ans;
  return 0;
}