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

int f(int l, int ll, int n, string s, vector<int>& bit, vector<int>& out) {
    int one = s.size() - count(s.begin(), s.end(), '0');
    int ans = 0;

    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);
}

signed main() {
    int 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 << endl;
        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 + 2 * n);
            bit.push_back(i + 3 * n);
        }
    }
    sort(bit.begin(), bit.end());

    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) && out[x % n] == 0)) x += 1;
            int ll = lower_bound(bit.begin(), bit.end(), x) - bit.begin();

            if (f(l, ll, n, s, bit, out) <= mid)
                ok = mid;
            else
                ng = mid;
        }
        ans = min(ans, anss + ok * n);
    }

    cout << ans << endl;
    return 0;
}