Six persons N, O, P, Q, R, and S sit in a linear row and face towards north direction. The distance between two adjacent persons is same in the row. R sits at an extreme end of the row. Only one person sits between R and N. N sits immediate left of S, who doesn't sit adjacent to R. P sits to the left of O. O doesn't sit adjacent to Q. If all the persons sit as per the alphabetical order from left to right end, then the position of how many persons remain unchanged?