public int WastedBinArea()
{
long usedSurfaceArea = 0;
for (int i = 0; i < usedRectangles.Count; ++i)
usedSurfaceArea += usedRectangles[i].width * usedRectangles[i].height;
return (int)((long)(binWidth * binHeight) - usedSurfaceArea);
}