Vaginal inspection of a parturient woman revealed: cervix dilation is up to 2 cm, fetal bladder is intact. Sacral cavity is free, sacral promontory is reachable only with a bent finger, the inner surface of the sacrococcygeal joint is accessible for examination. The fetus has cephalic presentation. Sagittal suture occupies the transverse diameter of pelvic inlet, the small fontanel to the left, on the side. What labor stage is this?