#include <iostream>

using namespace std;

int main()
{
    int ant=0, cur;
    int n;
    int nrt = 0;
    cin>>n;
    for(int i=1;i<=n;++i)
    {
        cin>>cur;
        if(cur==1 && ant == 1){
            ant = 0;
            nrt++;
        }
        else ant = cur;
    }
    cout<<nrt;
    return 0;
}