// Har Har Mahadev
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define int long long
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define repin rep(i,0,n)
#define precise(i) cout<<fixed<<setprecision(i)
#define vi vector<int>
#define si set<int>
#define mii map<int,int>
#define take(a,n) for(int j=0;j<n;j++) cin>>a[j];
#define give(a,n) for(int j=0;j<n;j++) cout<<a[j]<<' ';
#define vpii vector<pair<int,int>>
#define db double
#define be(x) x.begin(),x.end()
#define pii pair<int,int>
#define pb push_back
#define pob pop_back
#define ff first
#define ss second
#define lb lower_bound
#define ub upper_bound
#define bpc(x) __builtin_popcountll(x) 
#define btz(x) __builtin_ctz(x)
using namespace std;

using namespace __gnu_pbds;

typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
typedef tree<pair<int, int>, null_type,less<pair<int, int> >, rb_tree_tag,tree_order_statistics_node_update> ordered_multiset;

const long long INF=1e18;
const long long M=1e9+7;
const long long MM=998244353;
  
int power( int N, int M){
    int power = N, sum = 1;
    if(N == 0) sum = 0;
    while(M > 0){if((M & 1) == 1){sum *= power;}
    power = power * power;M = M >> 1;}
    return sum;
}
 
void solve()
{
    int n;
    cin >> n;
    string s;
    cin >> s;
    map<char,set<int>> m;
    repin{
        m[s[i]].insert(i);
    }
    int ans = INF;
    repin{
        if(s[i] != 'b')continue;
        auto q1 = m['s'].ub(i);
        if(q1 == m['s'].end())continue;
        auto q2 = m['u'].ub((*q1));
        if(q2 == m['u'].end())continue;
        auto p2 = m['p'].ub(i);
        if(p2 == m['p'].begin())continue;
        p2--;
        auto p1 = m['s'].ub(*p2);
        if(p1 == m['s'].begin())continue;
        p1--;
        int res = (*q1) + (*q2) - (*p1) - (*p2) - 6;
        ans = min(ans,res);
    }
    cout << ans << "\n";
}

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    #ifdef NCR
        init();
    #endif
    #ifdef SIEVE
        sieve();
    #endif
        solve();
    return 0;
}