Send encrypted emails to Satoshi Nakamoto for a month, helping him develop the Bitcoin code, hoping he would send you a donation (you can transfer the bitcoin private key to present) but without giving him information about the time of your assistance or any other information.

Bitcoin CPU mining on a laptop for 24 hours. You need to remember 3 private keys. But 1 of them will be the right one. You are not allowed to carry your laptop or keep any note paper in the present.