CodeForces - 1077B

#includ <cstdlib>
#include <cstdio>
#include <algorithm>

using namespace std;

int arr[10000];
int main(void)
{
    int n, ans = 0;
    cin >> n;
    for (int i = 0; i < n;i++)
        cin >> arr[i];
    for (int i = 1; i < n - 1;i++){
        if(arr[i - 1] == 1 && arr[i + 1] == 1 && arr[i] == 0){
            arr[i + 1] = 0;
            ans++;
        }
    }
    cout << ans;
    return 0;
}