How to set a limit to the sum of a set of dimensions

Hi,

I'm drawing a sketch to simulate a catenary that will host some cables:. It looks like this:

In my solidworks part (attached) I have two lines and an arc:

I know that the sum of the three lengths must be no more than 1500 mm, but they need to be free to move.

Is there a way to limit the sum of the three lengths ?

I tried using the belt/chain command, but it only allows you to simulate closed loops, while in this case it's an open loop.

Thanks for your help,

Alex

SolidworksSketching