What is the inverse of the following conditional statement?

"If the sum of the interior angles of a polygon is 180°, then the polygon is a triangle."

If the polygon is a triangle, then the sum of the interior angles of the polygon is 180°.
If the polygon is not a triangle, then the sum of interior angles of the polygon is not 180°.
If the sum of the interior angles of a polygon is not 180°, then the polygon is not a triangle.
If the sum of the interior angles of a polygon is 180°, then the triangle is a polygon.