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');
    assign(output,'xor_equ.out');
	reset(input);
    rewrite(output);
     read(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];
     write(max);
     close(input);
     close(output);
    end.