CO 30

Row 1: K
Row 2: P
Row 3: K
Row 4: P
Row 5: P
Row 6: K
Row 7: P
Row 8: K

Repeat 8 row pattern.

This is basically 4 rows of stockinette stitch followed by 4 rows of reverse stockinette stitch.

I slipped the first stitch of each row to create a selvedge.