#include <bits/stdc++.h>


using namespace std;


#define ll long long
#define flt double
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()


const ll inf = 1e18;
mt19937 rnd(234);


int32_t main() {
    if (1) {
        ios::sync_with_stdio(0);
        cin.tie(0);
        cout.tie(0);
    }
    int n;
    string s;
    cin >> n;
    cin >> s;
    vector<int> nxt(n), nxt2(n);
    vector<int> prvs(n), prvs2(n);
    for (int i = 0; i < n; i += 1) {
        if (s[i] == 's') {
            prvs2[i] = i;
        } else {
            prvs2[i] = i == 0 ? -1 : prvs2[i - 1];
        }
        if (s[i] == 'p') {
            prvs[i] = i;
        } else {
            prvs[i] = i == 0 ? -1 : prvs[i - 1];
        }
    }
    for (int i = n - 1; i >= 0; i -= 1) {
        if (s[i] == 's') {
            nxt[i] = i;
        } else {
            nxt[i] = i == n - 1 ? -1 : nxt[i + 1];
        }
        if (s[i] == 'u') {
            nxt2[i] = i;
        } else {
            nxt2[i] = i == n - 1 ? -1 : nxt2[i + 1];
        }
    }
    int rs = 10 * n;
    for (int i = 0; i < n; i += 1) {
        if (s[i] == 'b' and prvs[i] != -1 and prvs2[prvs[i]] != -1 and nxt[i] != -1 and nxt2[nxt[i]] != -1) {
            rs = min(rs, nxt[i] - i - 1 +
                nxt2[nxt[i]] - i - 2 +
                i - prvs[i] - 1 +
                i - prvs2[prvs[i]] - 2);
        }
    }
    cout << rs << "\n";
    return 0;
}