A hawker is stacking oranges for display. He first lays out a rectangle of 16 rows of 10 oranges each, then in the hollows between the oranges he places a layer consisting of 15 rows of 9 oranges. On top of this layer he places 14 rows of 8 oranges, and so on until the display is completed with a single line of oranges along the top. How many oranges does he use altogether?