{"raw_statement":[{"iden":"problem statement","content":"Takahashi is a user of a site that hosts programming contests.  \nWhen a user competes in a contest, the _rating_ of the user (not necessarily an integer) changes according to the _performance_ of the user, as follows:\n\n*   Let the current rating of the user be $a$.\n*   Suppose that the performance of the user in the contest is $b$.\n*   Then, the new rating of the user will be the avarage of $a$ and $b$.\n\nFor example, if a user with rating $1$ competes in a contest and gives performance $1000$, his/her new rating will be $500.5$, the average of $1$ and $1000$.\nTakahashi's current rating is $R$, and he wants his rating to be exactly $G$ after the next contest.  \nFind the performance required to achieve it."},{"iden":"constraints","content":"*   $0 \\leq R, G \\leq 4500$\n*   All input values are integers."},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$R$\n$G$"},{"iden":"sample input 1","content":"2002\n2017"},{"iden":"sample output 1","content":"2032\n\nTakahashi's current rating is $2002$.  \nIf his performance in the contest is $2032$, his rating will be the average of $2002$ and $2032$, which is equal to the desired rating, $2017$."},{"iden":"sample input 2","content":"4500\n0"},{"iden":"sample output 2","content":"\\-4500\n\nAlthough the current and desired ratings are between $0$ and $4500$, the performance of a user can be below $0$."}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}