conditional formatting highlight duplicates (when data is across two columns)

Hi There,

can someone help me out -

I need to apply conditional formatting to highlight when someone's name appears twice on my list (highlighting all entries) When the first name and surnames in separate columns Example attached


Thank you in advance

=if(sum(if($c$6:$c$2000&$d$6:$d$2000=$c6&$d6,1,0))+sum(if($c$6:$c$2000&$d$6:$d$2000=$d6&$c6,1,0))>1,1,0)