François Hollande, famous Cordon Bleu chef that he (like all French presidents) is, has invited a select few guests to his party, where he will be showing off the secret cheese-making process that doubles as a plan of attack against Britain. Your task as a UK spy (who happens to also be an Argentinian agent) is to steal this recipe for disaster. Entrance to the château wherein lies the party, however, is overseen by two guards. One guard always lies, and the other always tells the truth.
You arrive early and hide in some bushes. Guests begin approaching the door, and it becomes clear that there is some kind of password involved.
- One guest arrives by himself. “1”, says a guard. “6”, replies the guest. He is permitted entrance.
- Two more guests show up. “3” is prompted; “2” is the response, and it is apparently correct.
A group of seven is next to request entry, and the guards see fit to ask them each in turn.
- “2!” “7.”
- “11!” “6.”
- “20!” “4.”
- “4!” “2.”
- “6!” “3.”
The group had been doing fine until that last person, whose throat is promptly slit, along with those of what look to be his wife and son. “You were just off by one!”, says one of the guards, who looks like the sort of person who would tell the truth – but then again, it’s hard to tell with them. You’re not in Argentina anymore.
You think you’ve figured out the pattern, though, and are about to take your turn when another guest arrives, late. The challenge is given – “26” – but before the guest can give an answer, a loud gunshot is heard. Someone shouts out the window that the president is dead! It’s a coup d’état! You must get to the plans before the assassin, but one guard is still performing his duty. You are given the number five as a challenge; what is your response?