A company has a six-story office building. The company's finance department, planning department, administration department, sales department, human resources department, R & D department and other six departments work here, each department occupies one floor. It is known that: (1) the floors of the human resources department and the sales department are not adjacent; (2) the finance department is on the lower floor of the planning department; (3) the floor of the administration department is above the planning department, but below the human resources department.
The R & D department and sales department may be located on the first and second floors, respectively.