#include <iostream>

using namespace std;

const int nmax= 32000;

bool v[nmax+1];

int main(  ) {
    int n, sol= 0;
    cin>>n;
    for ( int i= 1; i<=n; ++i ) {
        cin>>v[i];
    }

    for ( int i= 1; i<=n; ++i ) {
        if ( v[i]&v[i+1] ) {
            v[i+1]= 0, ++sol;
        }
    }
    cout<<sol<<"\n";

    return 0;
}