I have a sheet of about 30000 lines, I am trying to find a way to highlight when I have the same entry in both column C and D eg.

23297 23297 H0572 C0154
23296 23296 H0572 G0083
21850 21850 H0681 S0729
21851 21851 H0681 S0730
23288 23288 H0571 S0705
23289 23289 H0571 S0706
21886 21886 H0681 S0694
21842 21842 H0681 S0728
23198 23198 H0703 S0312
23202 23202 H0704 G0037
23203 23203 H0704 G0088
23201 23201 H0704 S0312
23616 23616 H0705 C0161
34118 34118 H0705 C0161
23284 23284 H0570 G0083

So the red I would need highlighting, but not the blue as the H code is not the same

I hope that makes sense!