AUSTRIAN-POLISH 1997 Problem 3

Numbers $\frac{49}{1}, \frac{49}{2}, ... , \frac{49}{97}$ are writen on a blackboard. Each time, we can replace two numbers (like $a, b$ ) with $2ab-a-b+1$ . After $96$ times doing that prenominate action, one number will be left on the board. Find all the possible values fot that number.