Measured from the beginning of a proposed new highway, the Dist Auto mobile club have proposed to put an emergency telephone every dist. The Ance Automobile club have similarly proposed the same, but to every ance.

Also, measured from the beginning of the highway, there will be a milestone every mile.

There is an emergency telephone at the beginning of the highway.

How often will an extra telephone be required, if there is to be an emergency telephone between every two consecutive milestones?