#include <iostream>

using namespace std;

int main()
{
    int N, a = 0, b = 0;
    cin >> N;
    int cnt = 0;

    for( int i = 1; i <= N; ++i )
    {
        cin >> b;
        if( a && b )
            b = 0, cnt++;
        a = b;
    }

    cout << cnt;
    return 0;
}