You leap over the bone, and continue running. The zombie has given up his nasty bone attacks. After a few minutes of wild fleeing, you come across a cabin. It appears to be abandoned, but the lights are on. The door is locked with a bizarre mechanism. A piece of metal with three buttons and the engraving "I am a truly perfect heat engine. But I am not 100% efficient. I take place between 25K and 100K. How efficient am I?". Only a truly mad cabin owner would come up with such a silly lock. You can hear the zombie closing in behind you. Which button do you press?