Question 78
The central area of a town has the form of a $(2n+1) \times m$ rectangle, which is formed by $1 \times 1$ tiles. To illuminate the area, one-lamp lampposts are used. The lampposts are placed at the corners of some tiles, and each lamp illuminates the tiles having a corner at the lamppost position, and only those.
Find the smallest number of the lampposts required to illuminate the whole area, even if one of the lamps should burn out.
(E. Barabanov, M. Karpuk, A. Voidelevich)
Find the smallest number of the lampposts required to illuminate the whole area, even if one of the lamps should burn out.
(E. Barabanov, M. Karpuk, A. Voidelevich)