#include <bits/stdc++.h>
#define endl '\n'
#define pll pair<ll, ll>
#define tll tuple<ll, ll, ll>
#define vi vector<int>
#define vl vector<ll>
#define x first
#define y second
#define rep(i, j, k) for(int i = (j); i <= (k); i++)
#define per(i, j ,k) for(int i = (j); i >= (k); i--)
#define ios ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
using namespace std;
typedef long long ll;
const ll maxn = 2e5 + 10;
const ll mod = 998244353;
const ll inf = 0x3f3f3f3f;

void solve(){
	int n;
	string s;
	cin >> n >> s;
	vi pres(n), prep(n);
	vi afts(n), aftu(n);
	int ns = -1, np = -1;
	for (int i = 0; i < n; ++i){
		if (s[i] == 's') ns = i;
		if (s[i] == 'p') np = i;
		pres[i] = ns;
		prep[i] = np;
	}
	int as = -1, au = -1;
	for (int i = n - 1; i >= 0; --i){
		if (s[i] == 's') as = i;
		if (s[i] == 'u') au = i;
		afts[i] = as;
		aftu[i] = au;
	}
	int ans = inf;
	for (int i = 0; i < n; ++i)
		if (s[i] == 'b'){
			int tmp = 0;
			if (prep[i] != -1 && afts[i] != -1){
				if (pres[prep[i]] != -1 && aftu[afts[i]] != -1){
					tmp = i - prep[i] - 1 + i - pres[prep[i]] - 2 + afts[i] - i - 1 + aftu[afts[i]] - i - 2;
					ans = min(ans, tmp); 
				}
			}
		}
	cout << ans << endl;
	
}

int main(){
    ios;
    //freopen("sample.txt", "r", stdin);
    //freopen("resout.txt", "w", stdout);
    int t = 1;
    //cin >> t;
    while(t--){
        solve();
    }
    return 0;
}