Two analogies that relate places/locations to the associated travel mode is given in the form "A : B. C : ?". "A : B" relates place A to travel mode B. Your task is to replace the question mark (?) with the appropriate travel mode for the given place C, following the "A : B" relation.

Example Input: moon : rocket. museum : ?
Example Output: bus

Example Input: airport : train. island : ?
Example Output: boat

Example Input: mainland : boat. airport : ?
Example Output:
train