Restore the Lost Number

The number \(S\) is called the mean of two numbers \(R_1\) and \(R_2\) if \(S = \frac{R_1+R_2}{2}\). Mirko's birthday present for Slavko consisted of two integers \(R_1\) and \(R_2\). Slavko quickly computed their mean \(S\), which turned out to be an integer, but then he lost \(R_2\)! Your task is to help Slavko restore \(R_2\) given \(R_1\) and \(S\).

Note that mathematically, the value of \(R_2\) can be determined by rearranging the mean formula to get \(R_2 = 2S - R_1\).

inputFormat

The input contains two space-separated integers \(R_1\) and \(S\) on a single line.

outputFormat

Output a single integer \(R_2\) which is calculated using the formula \(R_2 = 2S - R_1\).

sample

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