Which statement is logically equivalent to the following conditional statement?

"If it has exactly four sides, then it is not a hexagon."

If it does not have exactly four sides, then it is not a hexagon.
If it does not have exactly four sides, then it is a hexagon.
If it is a hexagon, then it does not have exactly four sides.
If it is not a hexagon, then it has exactly four sides.

If it is not a hexagon, then it has exactly four sides.