#include <iostream>

using namespace std;
int n,sol1,sol2,v[32004],a[32004];
int main()
{
    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]){sol1++;v[i+1]=(v[i]+1)%2;}

    cout<<sol1<<"\n";
    return 0;
}