19134번 - 2ドルx + 2$ 다국어

문제

bobo has $n$ integers 1,ドル 2, \dots, n$ and uses them to play a game.

He would like to choose a subset $S$ of $\{1, 2, \dots, n\}$ such that for all $x \in S,ドル $(2x + 2) \notin S$.

Now he is curious about the maximum size of $S$.

입력

The first line contains an integer $n$ (1ドル \leq n < 10^{100})$.

출력

A single integer denotes the maximum size.

제한

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