4. Subjects who are scheduled to undergo colonoscopy in the morning will take colonoscopy preparation medication (2L (liter) of polyethylene glycol with ascorbic acid) in a split dose (i.e. 1L from 8-10 pm of the day before colonoscopy and 1L 4-6 hours before colonoscopy). Those who will undergo colonoscopy in the afternoon will take 2L of the preparation medication 6 hours before colonoscopy.