#include <iostream>
using namespace std;
int main()
{
	int n, i, a[32000], y, r = 0;
	cin >> n;
	for (i = 0; i < n; i++)
	{
		cin >> a[i];
	}
	for (i = 0; i < n; i++)
	{ 
		if (a[i] == 1 && a[i + 1] == 1)
		{
			a[++i] = 0;
			r++;
		}
	}
	cout << r;



}