Coding is the closest thing we have to superpower ！
已知R_{1}和R_{2}的平均数为S，即\left(R_{1}+R_{2}\right) / 2=S
现在已知R_{1}和S，求R_{2}。
输入两个整数R_{1}和S，-1000\le R_1,S \le 1000.
输出R_{2}
11 15
19
4 3
2