static int Fish(int[] a, int[] b)
{
    var size = a.Length;
    var dead = 0;
    var fish = new Stack<int>();

    for (int i = 0; i < size; i++)
    {
        if (b[i] == 1)
        {
            fish.Push(a[i]);
        }
        else
        {
            while (fish.Count > 0)
            {
                dead++;
                if (a[i] > fish.Peek())
                {
                    fish.Pop();
                }
                else
                {
                    break;
                }
            }
        }
    }

    return size - dead;
}