#include <bits/stdc++.h>

#define int long long

void solve() {
    int n;
    std::cin >> n;
    std::string s;
    std::cin >> s;
    
    std::vector<std::vector<int>> pre(n + 1, std::vector<int>(32, -1));
    auto nex = pre;

    pre[0][s[0] - 'a'] = 0;
    for(int i = 1; i < n; ++i) {
        for(char c = 'a'; c <= 'z'; c++) {
            pre[i][c - 'a'] = pre[i - 1][c - 'a'];
        }
        pre[i][s[i] - 'a'] = i;
    }
    nex[n - 1][s[n - 1] - 'a'] = n - 1;
    for(int i = n - 2; i >= 0; i--) {
        for(char c = 'a'; c <= 'z'; c++) {
            nex[i][c - 'a'] = nex[i + 1][c - 'a'];
        }
        nex[i][s[i] - 'a'] = i;
    }

    int ans = 1e16;
    for(int i = 0; i < n; i++) {
        int sum = 0;
        if(s[i] == 'b') {
            int p = pre[i]['p' - 'a'];
            if(p == -1) continue;
            sum += (i - 1) - p;
            int s1 = pre[p]['s' - 'a'];
            if(s1 == -1) continue;
            sum += (i - 2) - s1;
            int s2 = nex[i]['s' - 'a'];
            if(s2 == -1) continue;
            sum += s2 - (i + 1);
            int u = nex[s2]['u' - 'a'];
            if(u == -1) continue;
            sum += u - (i + 2);
            ans = std::min(ans, sum);
        }
    }
    std::cout << ans << '\n';
}

signed main() {
   // std::ios::sync_with_stdio(false);
    //std::cin.tie(nullptr);

    int t = 1;
    // std::cin >> t;
    for (int i = 0; i < t; ++i) {
        solve();
    }

    return 0;
}