#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <iomanip>
#include <utility>
#include <tuple>
#include <functional>
#include <bitset>
#include <cassert>
#include <complex>
#include <stdio.h>
#include <time.h>
#include <numeric>
#include <random>
#include <unordered_set>
#include <unordered_map>
#define all(a) a.begin(), a.end()
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define range(i, a, b) for (ll i = (a); i < (b); i++)
#define pb push_back
#define debug(x) cerr << __LINE__ << ' ' << #x << ':' << (x) << '\n'
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;
typedef complex<ld> com;
template<class T> using pri_s = priority_queue<T, vector<T>, greater<T>>;
template<class T> using pri_b = priority_queue<T>;
constexpr int inf = 1000000010;
constexpr ll INF = 1000000000000000010;
constexpr int mod1e9 = 1000000007;
constexpr int mod998 = 998244353;
constexpr ld eps = 1e-12;
constexpr ld pi = 3.141592653589793238;
constexpr ll ten(int n) { return n ? 10 * ten(n - 1) : 1; };
int dx[] = { 1,0,-1,0,1,1,-1,-1 }; int dy[] = { 0,1,0,-1,1,-1,1,-1 };
ll mul(ll a, ll b) { return (a > INF / b ? INF : a * b); }
void fail() { cout << "-1\n"; exit(0); } void no() { cout << "No\n"; exit(0); }
template<class T> void er(T a) { cout << a << '\n'; exit(0); }
template<class T, class U> inline bool chmax(T &a, const U &b) { if (a < b) { a = b; return true; } return false; }
template<class T, class U> inline bool chmin(T &a, const U &b) { if (a > b) { a = b; return true; } return false; }
template<class T> istream &operator >> (istream &s, vector<T> &v) { for (auto &e : v) s >> e; return s; }
template<class T> ostream &operator << (ostream &s, const vector<T> &v) { for (auto &e : v) s << e << ' '; return s; }
template<class T, class U> ostream &operator << (ostream &s, const pair<T, U> &p) { s << p.first << ' ' << p.second; return s; }

struct fastio {
	fastio() {
		cin.tie(0); cout.tie(0);
		ios::sync_with_stdio(false);
		cout << fixed << setprecision(20);
		cerr << fixed << setprecision(20);
	}
}fastio_;

template<class T> class segtree {
	int n;
	vector<T> data;
	T id = 0;
	T operation(T a, T b) { return a + b; };
public:
	segtree(int _n) {
		n = 1;
		while (n < _n + 2) n <<= 1;
		data = vector<T>(2 * n, id);
	}
	segtree(vector<T> vec) {
		int _n = vec.size();
		n = 1;
		while (n < _n + 2) n <<= 1;
		data = vector<T>(2 * n, id);
		for (int i = 0; i < _n; i++) data[i + n] = vec[i];
		for (int i = n - 1; i >= 1; i--) data[i] = operation(data[i << 1], data[i << 1 | 1]);
	}
	void change(int i, T x) {
		i += n;
		data[i] = x;
		while (i > 1) {
			i >>= 1;
			data[i] = operation(data[i << 1], data[i << 1 | 1]);
		}
	}
	void add(int i, T x) { change(i, data[i + n] + x); }
	T get(int a, int b) {
		T left = id; T right = id;
		a += n; b += n;
		while (a < b) {
			if (a & 1) left = operation(left, data[a++]);
			if (b & 1) right = operation(data[--b], right);
			a >>= 1; b >>= 1;
		}
		return operation(left, right);
	}
	T get_all() { return data[1]; }
	T operator[](int i) { return data[i + n]; }
};

ll solve1(int n, string s) {
	string g = s;
	sort(all(g));
	map<string, int> mp;
	queue<string> que;
	que.push(s);
	mp[s] = 0;
	while (!que.empty()) {
		string str = que.front(); que.pop();
		string a = str.back() + str.substr(0, n - 1);
		string b = a;
		swap(b[0], b[1]);
		if (!mp.count(a)) {
			mp[a] = mp[str] + 1;
			que.push(a);
		}
		if (!mp.count(b)) {
			mp[b] = mp[str] + 1;
			que.push(b);
		}
	}
	return mp[g];
}

ll solve(ll n, string s) {
	assert(2 <= n && n <= ten(5));
	rep(i, n) assert(s[i] == '0' || s[i] == '1');
	vector<ll> one;
	rep(i, n) if (s[i] == '1') one.pb(i);
	ll sz = one.size();
	if (sz == 0) return 0;
	rep(i, sz) one.pb(one[i] + n);
	vector<ll> d;
	d.pb(0);
	rep(i, 2 * sz - 1) d.pb(one[i + 1] - one[i] - 1);
	rep(i, 2 * sz - 1) d[i + 1] += d[i];
	segtree<ll> seg(2 * n);
	rep(i, sz) seg.add(d[i], 1);
	vector<bool> check(sz);
	rep(i, sz) check[i] = (sz - i + one[i] == n);
	ll ans = INF;
	rep(i, sz) {
		ll res = 0;
		if (s[0] == '1' && s[n - 1] == '1' && check[i]) {
			int f = 1;
			ll ok = n, ng = 1;
			while (ok - ng > 1) {
				ll mid = (ok + ng) / 2;
				ll r = mid - 1 + d[i];
				ll g = seg.get(r + 1, 2 * n);
				if (d[sz - 1] - d[i] <= mid - 1 && g != 0) g++;
				if (g <= mid) ok = mid;
				else ng = mid;
			}
			{
				ll r = d[i];
				ll g = seg.get(r + 1, 2 * n);
				if (d[sz - 1] - d[i] <= 0 && g != 0) g++;
				if (chmin(ok, g)) f = 0;
			}
			res = ok * n;
			res -= one[i];
			res += n - sz - ok;
			res += f;
			//debug(res);
			//debug(ok);
		}
		else {
			ll ok = n, ng = -1;
			while (ok - ng > 1) {
				ll mid = (ok + ng) / 2;
				ll r = mid + d[i];
				ll g = seg.get(r + 1, 2 * n);
				if (d[sz - 1] - d[i] <= mid && g != 0) {
					g++;
					if (s[0] == '1' && s[n - 1] == '0' && g != 0 && d[sz] - d[i] > mid) g--;
				}
				if (g <= mid) ok = mid;
				else ng = mid;
			}
			res = ok * n;
			res -= one[i];
			res += n - sz - ok;
			//debug(res);
			//debug(ok);
		}
		//debug(res);
		if (res < 0) res += n;
		chmin(ans, res);
		seg.add(d[i], -1);
		seg.add(d[i + sz], 1);
	}
	return ans;
}

int main() {
	int n;
	cin >> n;
	string s;
	cin >> s;
	cout << solve(n, s) << '\n';
}