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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
#define SZ(v) ((int)(v).size())

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(15);
    }
} setupio;

template <class T>
vector<pair<T, int>> RLE(const vector<T> &v) {
    vector<pair<T, int>> res;
    for (const auto x : v) {
        if (res.size() == 0 || res.back().first != x) {
            res.emplace_back(x, 1);
        } else {
            res.back().second++;
        }
    }
    return res;
}

vector<pair<char, int>> RLE(const string &s) {
    vector<char> v;
    for (const char &c : s) {
        v.emplace_back(c);
    }
    return RLE(v);
}

int main() {
    int n;
    string s;
    cin >> n >> s;
    auto rle = RLE(s);
    int ans = 0;
    rep(i, SZ(rle)) {
        if (rle[i].first == '1') { continue; }
        if (rle[i].second >= 2) {
            ans += (rle[i].second + 1) / 2;
        } else {
            if (i + 2 < SZ(rle) && rle[i + 1].second == 1 && rle[i + 2].second == 1) {
                ans++;
            }
        }
    }
    cout << ans << "\n";
}