if they had 2 pieces of wood (or more) which were 9.5 meters in summary, they need to put the 1st piece into river and take the 2nd with them, then put 2nd in front of 1st, then go to the 2nd and take 1st, and then put 1st in front of the 2nd... that's all...
P.S. it's only if they had 2 pieces of wood
