Assignment:
A contractor for a Paradise city on the XYZ planet has to order traffic lights for the city. All streets in the city are straight and infinitely long in both directions. No matter how many streets have the same crossing, there will be a need for only one traffic light per crossing. Knowing only the number of streets n, how many traffic lights will the contractor need to order to make sure he will not run out lights.
Provide complete and step by step solution for the question and show calculations and use formulas.