思维测试

Toy Army

Time Limit:2000MS    Memory Limit:262144KB    64bit IO Format:%I64d & %I64u

SubmitStatus

Description

The hero of our story, Valera, and his best friend Arcady are still in school, and therefore they spend all the free time playing turn-based strategy "GAGA: Go And Go Again". The gameplay is as follows.

There are two armies on the playing field each of which consists ofn men (n is always even). The current player specifies for each of her soldiers an enemy's soldier he will shoot (a target) and then all the player's soldiers shot simultaneously. This is a game world, and so each soldier shoots perfectly, that is he absolutely always hits the specified target. If an enemy soldier is hit, he will surely die. It may happen that several soldiers had been indicated the same target. Killed soldiers do not participate in the game anymore.

The game "GAGA" consists of three steps: first Valera makes a move, then Arcady, then Valera again and the game ends.

You are asked to calculate the maximum total number of soldiers that may be killed during the game.

Input

The input data consist of a single integer n (2 ≤ n ≤ 10⁸,n is even). Please note that before the game starts there are2n soldiers on the fields.

Output

Print a single number — a maximum total number of soldiers that could be killed in the course of the game in three turns.

Sample Input

Input

2

Output

3

Input

4

Output

6

Hint

The first sample test:

1) Valera's soldiers 1 and 2 shoot at Arcady's soldier 1.

2) Arcady's soldier 2 shoots at Valera's soldier 1.

3) Valera's soldier 1 shoots at Arcady's soldier 2.

There are 3 soldiers killed in total: Valera's soldier 1 and Arcady's soldiers 1 and 2.

题意：

共有三次开枪机会，每次可以为任何人选定唯一敌人（a的敌人是b,b的敌人是a的情况是错误的）；

三次开枪后，求最多能死几人？

解题：

第一次：a方瞄准b方一半：

第二次：b方剩余一半瞄准a方一半：

第三次：a方剩余一半瞄准b方剩余的一半：

代码：

#include<stdio.h>  int main()  {  int n,result;  scanf("%d",&n);  result=(n/2)*3;  printf("%d",result);  return 0;  }