#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define db double
#define pii pair<int,int>
#define pli pair<ll,int>
#define pil pair<int,ll>
#define pll pair<ll,ll>
#define ti3 tuple<int,int,int>
#define int128 __int128_t
#define pii128 pair<int128,int128>
const int inf = 1 << 30;
const ll linf = 1e18;
const ll mod = 1e9 + 7;
const db EPS = 1e-10;
const db pi = acos(-1);
template<class T> bool chmin(T& x, T y){
    if(x > y) {
        x = y;
        return true;
    } else return false;
}
template<class T> bool chmax(T& x, T y){
    if(x < y) {
        x = y;
        return true;
    } else return false;
}

// overload macro
#define CAT( A, B ) A ## B
#define SELECT( NAME, NUM ) CAT( NAME, NUM )

#define GET_COUNT( _1, _2, _3, _4, _5, _6 /* ad nauseam */, COUNT, ... ) COUNT
#define VA_SIZE( ... ) GET_COUNT( __VA_ARGS__, 6, 5, 4, 3, 2, 1 )

#define VA_SELECT( NAME, ... ) SELECT( NAME, VA_SIZE(__VA_ARGS__) )(__VA_ARGS__)

// rep(overload)
#define rep( ... ) VA_SELECT(rep, __VA_ARGS__)
#define rep2(i, n) for (int i = 0; i < int(n); i++)
#define rep3(i, a, b) for (int i = a; i < int(b); i++)
#define rep4(i, a, b, c) for (int i = a; i < int(b); i += c)

// repll(overload)
#define repll( ... ) VA_SELECT(repll, __VA_ARGS__)
#define repll2(i, n) for (ll i = 0; i < ll(n); i++)
#define repll3(i, a, b) for (ll i = a; i < ll(b); i++)
#define repll4(i, a, b, c) for (ll i = a; i < ll(b); i += c)

// rrep(overload)
#define rrep( ... ) VA_SELECT(rrep, __VA_ARGS__)    
#define rrep2(i, n) for (int i = n - 1; i >= 0; i--)
#define rrep3(i, a, b) for (int i = b - 1; i >= a; i--)
#define rrep4(i, a, b, c) for (int i = b - 1; i >= a; i -= c)

// rrepll(overload)
#define rrepll( ... ) VA_SELECT(rrepll, __VA_ARGS__)
#define rrepll2(i, n) for (ll i = n - 1; i >= 0ll; i--)
#define rrepll3(i, a, b) for (ll i = b - 1; i >= ll(a); i--)
#define rrepll4(i, a, b, c) for (ll i = b - 1; i >= ll(a); i -= c)

// for_earh
#define fore(e, v) for (auto&& e : v)

// vector
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()

int n;
string s;
ll ans[100010];
int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    cin >> n >> s;
    
    rep (i, n) ans[i] = (s[i] == 'b' ? 0 : inf);
    
    ll prep = -inf;
    vector<ll> pres;
    pres.push_back(-inf);
    int idx = 0;

    rep (i, n) {
        if (s[i] == 's') pres.push_back(i);
        if (s[i] == 'p') {
            prep = i;
            while (idx + 1 < (int)pres.size() && pres[idx + 1] < prep) idx++;
        }
        if (s[i] == 'b') ans[i] += i - 1 - prep + i - 2 - pres[idx];
    }

    ll poss = inf;
    vector<ll> posu;
    posu.push_back(inf);
    idx = 0;
    rrep (i, n) {
        if (s[i] == 'b') ans[i] += poss - i - 1 + posu[idx] - i - 2;
        if (s[i] == 's') {
            poss = i;
            while (idx + 1 < (int)posu.size() && posu[idx + 1] > poss) idx++;
        }
        if (s[i] == 'u') posu.push_back(i);
    }

    cout << *min_element(ans, ans + n) << endl;
    
}