666÷[(6+6)÷6]×6+6÷6+6-6=1999
666÷[(6+6)÷6]×6+6÷6+6-6
=666÷(12÷6)×6+1+6-6
=666÷2×6+1+0
=333×6+1+0
1998+1
=1999