#include <bits/stdc++.h>
#define int __int128
using namespace std;

signed main() {
    long long n;
    cin >> n;
    string s;
    cin >> s;
    int ans = 1e10;

    int zero = count(s.begin(), s.end(), '0');
    int one = n - zero;
    if (zero == 0 || zero == n) {
        cout<<0;return 0;
    }

    vector<int> out(n, 0);
    if (s[0] == '1') {
        out[0] = 1;
        for (int i = n - 1; i >= 0; i--) {
            if (s[i] == '1') {
                out[i] = 1;
            } else {
                break;
            }
        }
    }

    vector<int> bit;
    for (int i = 0; i < n; i++) {
        if (s[i] == '1') {
            bit.push_back(i);
            bit.push_back(i + n);
            bit.push_back(i + n + n);
            bit.push_back(i + n + n + n);
        }
    }
    sort(bit.begin(), bit.end());

    auto f = [&](int l, int ll) {
        int sp_l = (l + one) % n;
        int sp_r = n;
        if (sp_l == 0) {
            sp_l = n;
        }

        int ansl = 0;
        if (bit[ll] <= l + n) {
            if (sp_l <= ((bit[ll] - 1) % n + 1) && ((bit[ll] - 1) % n + 1) <= sp_r && out[bit[ll] % n] == 0) {
                ansl = l + n - bit[ll] - 1;
            } else {
                ansl = l + n - bit[ll];
            }
        }

        int ansr = 0;
        if (l + n + one - 1 < bit[ll + one - 1]) {
            int ng = -1;
            int ok = one;
            while (ng + 1 != ok) {
                int mid = (ng + ok) / 2;
                if (l + n + mid < bit[ll + mid]) {
                    ok = mid;
                } else {
                    ng = mid;
                }
            }

            bool flag1 = true;
            bool flag2 = false;
            int x = l + n + ok;
            if (x % n != 0) {
                x += n - (x % n);
            }
            if (x <= l + n + one - 1) {
                if (l + n + ok <= bit[ll + ok] && bit[ll + ok] <= x) {
                    flag2 = true;
                }
                x += n;
            }
            if (l + n + ok <= bit[ll + ok] && bit[ll + ok] <= x) {
                flag1 = false;
            }
            ansr = one - ok + flag1 - flag2;
        }
        return max(ansl, ansr);
    };

    for (int l = 0; l < n; l++) {
        int anss = (-l - one) % n;

        int sp_l = (l + one) % n;
        int sp_r = n;
        if (sp_l == 0) {
            sp_l = n;
        }

        int ng = -1;
        int ok = n;
        while (ng + 1 != ok) {
            int mid = (ng + ok) / 2;

            int x = l + n - mid - 1;
            if (!(sp_l <= ((x - 1) % n + 1) && ((x - 1) % n + 1) <= sp_r && out[x % n] == 0)) {
                x += 1;
            }
            int ll = lower_bound(bit.begin(), bit.end(), x) - bit.begin();
            if (f(l, ll) <= mid) {
                ok = mid;
            } else {
                ng = mid;
            }
        }
        ans = min(ans, anss + ok * n);
    }
    cout << (long long)ans;

    return 0;
}