Display Cable from Dell (S2718D) to MacBookPro 2018

Hi!

I just got a new 2018 15" MacBookPro. I would like to connect a Dell S2718D monitor to it, but am a bit confused as to which cable to purchase. The monitor is missing the cable that came with it, so I tried a generic USB3.1 Type-C Male to HDMI Type-A male adapter cable 4K*2K30HZ, and the screen sometimes flickers and displays horizontal multi-colored lines. I then tried a generic USB-C to USB-C cable and it works for a short time, but flickers out.

Can someone suggest a proper cable from the monitor to the new MacBookPro 2018 15", please?

Thanks!