#include <bits/stdc++.h>
#define endl '\n'
using namespace std;

const int MAXN = 1e5 + 5;

int main ()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    freopen("freddy.in", "r", stdin);
    freopen("freddy.out", "w", stdout);

    int n;
    cin >> n;

    string s;
    cin >> s;

    int i = 0;

    int ans = 0;

    while (i < n)
    {
        while (s[i] == '0') i++;

//        int i = -1;
        bool notReady = false;


//        for (int j = 0; j < n; j++)
//            if (s[j] == '0' && i != -1) notReady = true;
//            else
//            if (s[j] == '1' && i == -1)
//            {
//                i = j;
//            }

//        if (!notReady) break;


        int cnt = 0;

        int start = i;

        ans++;

//        cerr << "_ " << i << endl;

        int j;
        for (j = i; j < n ; j++)
        {

//            cerr << "k";
            if (s[j] == '1' )
            {
                if (cnt == 2 )
                {
//                    cerr << i << " " << start << " " << j << endl;
//                    cerr << s << endl;
                    reverse(s.begin() + start, s.begin() + j-0);

//                    cerr << s << endl;
                    i = j;
                    break;
                }
                cnt = 1;
            }
            else if (j == n-1)
            {
//                cerr << "e\n";
//                    cerr << i << " " << start << " " << j << endl;
//                    cerr << s << endl;
                    reverse(s.begin() + start, s.end());
//                    cerr << s << endl;
                    i = j;
                    break;
            }
            else if (s[j] == '0') cnt = 2;
        }
        i = j;
//        cerr << s << endl;

//        i++;
    }
//    cerr << s << endl;

    cout << ans-1 << endl;

    return 0;
}

/**
20
01010001100010011010

*/