[pbInfo] nrnod

#include <fstream>
using namespace std;

ifstream fin("nrnod.in");
ofstream fout("nrnod.out");

int a[100000], sol;

int main()
{
    int i = 2;
    while(fin >> a[i])
    {
        if((a[i] != 0 && a[i - 1] == 0 && a[i - 2] != 0) || (a[i] == 0 && a[i - 1] == 0 && a[i - 2] == 0)) sol++;
        i++;
    }
    fout << sol;
    return 0;
}