题意翻译
设S=(R1+R2)/2，给定R1与S (-1000<=R1,S<=1000)(−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 按照fhq大神的话来说
这题还用做？
#include<cstdio>
using namespace std;
const int MAXN = ;
inline int read() {
char c = getchar(); int x = , f = ;
while(c < '' || c > '') { if(c == '-')f = -; c = getchar(); }
while(c >= '' && c <= '') x = x * + c - '', c = getchar();
return x * f;
}
int main() {
#ifdef WIN32
freopen("a.in", "r", stdin);
#endif
int R1 = read(), S = read();
printf("%d", * S - R1);
return ;
}