In my program there is such a fragment:

Cs:array[1..10][1..100]of byte;
...

read(n); fillchar(Cs,sizeof(Cs),0);
for i:=1 to n do begin
  read(k,l); if Cs[l,k]>0 then MakeCrash; Cs[l,k]:=i;
end;
...

where MakeCrash is procedure which makes some crash(MLE,divide by zero...)

And this program got CRASH on test #13. When i'v deleted MakeCrash ,it got WA#18.
It may happens only if there is the same cards in input, but it is impossible due to the problem.