var n,i,j:longint;max:int64;
a:array[1..100000] of int64;
procedure sort(l,r: longint);
      var
         i,j,x,y: longint;
      begin
         i:=l;
         j:=r;
         x:=a[(l+r) div 2];
         repeat
           while a[i]<x do
            inc(i);
           while x<a[j] do
            dec(j);
           if not(i>j) then
             begin
                y:=a[i];
                a[i]:=a[j];
                a[j]:=y;
                inc(i);
                j:=j-1;
             end;
         until i>j;
         if l<j then
           sort(l,j);
         if i<r then
           sort(i,r);
      end;
begin
assign(input,'xor_equ.in');
reset(input);
assign(output,'xor_equ.out');
rewrite(output);
 readln(n);
 for i:=1 to n do
  read(a[i]);
 sort(1,n);
 max:=0;
 if n<3 then begin max:=a[1]xor a[2];if a[2] xor a[3]>max then max:=a[2]xor a[3];if a[1]xor a[3]>max then max:=a[1]xor a[3];writeln(max);halt; end;
 for i:=1 to (n div 4)+2 do
  for j:=1 to (n div 4)+2 do
  if (a[i] xor a[n-j+1]>max) and (i<>j) then max:=a[i] xor a[n-j+1];
 writeln(max);
 close(input);
 close(output);
end.