Drunk Student #1

A drunk student is on a 100-meter-long bridge. He is at the 27th meter, so he has still 73 meters in front of him. He is so drunk that he has a 50% probability of staggering a meter forward and a 50% probability of staggering a meter backward. What is the probability that he will make it to the end of the bridge before he reaches the starting point? Try involving martingale theory in your solution.

Answer format: round to 2 decimal places.