There is a river which can be considered as an infinitely long straight line with width W.

There are A piles on the river, and B types of wooden disks are available. The location of the i-th pile is (Xi, Yi).

The i-th type of wooden disks has radius Ri, and its price is Ci per disk.

Disks can be placed on the river such that for each wooden disk, its center must be one of the locations (Xi, Yi) of piles. We can only move on the wooden disks.

How to find the minimum cost such that we can cross the river? I am unable to approach questions like these. What would be the best method to approach this one?