# [COCI2006-2007#2] R2

## 题意翻译

设S=(R1+R2)/2，给定R1与S $(-1000<=R1,S<=1000)$，求R2。
感谢@Xeonacid 提供的翻译

## 题目描述

The number S is called the mean of two numbers R1 and R2 if S is equal to (R1+R2)/2. Mirko's birthday present for Slavko was two integers R1 and R2. Slavko promptly calculated their mean which also happened to be an integer but then lost R2! Help Slavko restore R2.

## 输入输出格式

### 输入格式

The first and only line of input contains two integers R1 and S, both between -1000 and 1000.

### 输出格式

Output R2 on a single line.

## 输入输出样例

### 输入样例 #1

`11 15`

### 输出样例 #1

`19`

### 输入样例 #2

`4 3`

### 输出样例 #2

`2`