CF440A Forgotten Episode

Polycarpus adores TV series. Right now he is ready to finish watching a season of a popular sitcom "Graph Theory". In total, the season has $ n $ episodes, numbered with integers from $ 1 $ to $ n $ . Polycarpus watches episodes not one by one but in a random order. He has already watched all the episodes except for one. Which episode has Polycaprus forgotten to watch?

The first line of the input contains integer $ n $ $ (2

Print the number of the episode that Polycarpus hasn't watched.