IMO 1992 LL ITA40

The colonizers of a spherical planet have decided to build N

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IMO 1992 LL ITA40

Origin: ITA

Problem

The colonizers of a spherical planet have decided to build N towns, each having area 1/1000 of the total area of the planet. They also decided that any two points belonging to different towns will have different latitude and different longitude. What is the maximal value of N?