Virtual contest is a way to take part in past contest, as close as possible to participation on time. It is supported only ACM-ICPC mode for virtual contests.
If you've seen these problems, a virtual contest is not for you - solve these problems in the archive.
If you just want to solve some problem from a contest, a virtual contest is not for you - solve this problem in the archive.
Never use someone else's code, read the tutorials or communicate with other person during a virtual contest.

No tag edit access

B. Segments

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputYou are given an integer *N*. Consider all possible segments on the coordinate axis with endpoints at integer points with coordinates between 0 and *N*, inclusive; there will be of them.

You want to draw these segments in several layers so that in each layer the segments don't overlap (they might touch at the endpoints though). You can not move the segments to a different location on the coordinate axis.

Find the minimal number of layers you have to use for the given *N*.

Input

The only input line contains a single integer *N* (1 ≤ *N* ≤ 100).

Output

Output a single integer - the minimal number of layers required to draw the segments for the given *N*.

Examples

Input

2

Output

2

Input

3

Output

4

Input

4

Output

6

Note

As an example, here are the segments and their optimal arrangement into layers for *N* = 4.

Codeforces (c) Copyright 2010-2018 Mike Mirzayanov

The only programming contests Web 2.0 platform

Server time: Aug/21/2018 13:46:01 (f2).

Desktop version, switch to mobile version.

User lists

Name |
---|