Given a math word problem, answer the following question. You might need to apply addition or subtraction mathematical operators on the numbers embedded in the text to answer the question and then only report the final numerical answer.

Example input: robin bought 11 sodas for her and her friends . if they only drank 3 of them how many extras did she have ?
Example output: 8
Example explanation: Extra sodas is total - drank = 11-3 = 8
Q: the map led them through the forest and into a cave . to open the cave doors they need to put weights on the switch . if the switch already has 234 lbs . of weights and the total needed is 712 lbs . how much more weight to they need to add ?
A:
478