In ancient time there was a city named Maya. In Maya, there are lights everywhere on the roads. The source of light is incandescent light bulbs. A lamp post contains multiple incandescent light bulbs. Suddenly, a storm went over the city with high-speed wind and some of the light bulbs destroyed. The governor of the city is a perfectionist. He wants to re-decorate the light bulbs as soon as possible. He wants an equal number of light bulbs in every lamp post and the cost of removing or adding a light bulb is the same. A specialist suggested to the governor that, a single action either adding or removing the light bulbs should be done for quick re-decoration of all the lamp posts. The specialist also suggested an action that costs less.
This is a companion discussion topic for the original entry at https://toph.co/p/city-of-lights