Given the task definition, example input & output, solve the new input case.
In this task, you will be presented with a question and you have to answer the question based on your knowledge. Your answers should be as short as possible.
Example: Who were the builders of the mosque in Herat with fire temples ?
Output: Ghurids
This is a good example. Ghurids were the builders of the mosque in Herat with fire temples.

New input case for you: What year was the tallest building in Philadelphia open to the public ?
Output:
2018