10551055 SUSTech Online Judge
Problem 1055 --Destroy all balls

1055: Destroy all balls

Time Limit: 1 Sec  Memory Limit: 128 MB
Submit: 81  Solved: 38
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Description

There are n boxes in a line. At first, each box contains only one ball. There is a special machine. For each operation, the machine can attack a box. Once a ball is attacked, it will jump into the adjacent boxes. When a ball is attacked by twice, it will be destroyed. Please find the minimum number of operations that can destroy all balls.

Input

Only one line with an integer n. (2 <= n <= 105)

Output

One line contains the minimum number of operations that can destroy all balls.

Sample Input

2

Sample Output

3

HINT

Source

Bonus_Lab 

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