#include <iostream>
#include <algorithm>

using namespace std;

int N;
int A[32002], result;

int main()
{
    cin >> N;
    for (int i = 1; i <= N; ++i)
    {
        cin >> A[i];
        if (A[i] == 1 && A[i - 1] == 1)
        {
            A[i] = 0;
            ++result;
        }
    }

    cout << result << '\n';
}