246. Black & White

time limit per test: 0.25 sec.
memory limit per test: 65536 KB
input: standard
output: standard



Consider a necklace made of 2N-1 black and white beads, K of which are black. Necklace is called "beautiful" if it is possible to choose two black beads (not necessarily different) in such a way that one of two necklace parts strictly between them contains exactly N beads.
For example, if N=4 and K=3, necklace "WBWBWBW" is beautiful, and necklace "BBWWBWW" is not.
You need to find minimal K for which every necklace of 2N-1 beads is beatiful.

Input
The first line of input contains odd integer number 2N-1 (5<=2N-1<=2^31-1).

Output
Output minimal K for which every necklace of 2N-1 beads is beatiful.

Sample test(s)

Input
Test #1 
5 
 
Test #2 
7 

Output
Test #1 
3 
 
Test #2 
4 
  
  
Author:Alexey Preobrajensky 
Resource:Petrozavodsk Summer Training Sessions 2004 
Date:August 25, 2004