program pol;
var a,b:array[1..200] of integer; i,j,n,k:integer;
f,p:text;
begin
     assign(f,'Palindro.dat');
     reset(f);
     readln(f,n);
     for i:=1 to n*2-1 do
     begin
          read(f,a[i])
     end;
     close(f);
    { if n div 2<>0 then a[n div 2+1]:=0}

     i:=1;   k:=1; j:=n*2-1;
     while j<>0 do
     begin
          if  a[i]<>a[j] then begin b[k]:=a[i]; i:=i+1; k:=k+1 end
          else i:=i+1;
          j:=j-1
     end;

     for i:=1 to n do
     begin
          if b[i]<>0 then k:=k+1
          else k:=k+0
     end;
     k:=k-1;
     for i:=1 to k do
     begin if b[i]=b[i-1] then  k:=k-1 end;

      k:=k-1;
      assign(p,'Palindro.sol');
     rewrite(p);
      writeln(p,k);
     while k<>0 do
     begin
         write(p,b[k],' ');
         k:=k-1
     end;
         close(p)
end.