题解 | 牛牛的等差数列

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a,b;
        a = in.nextInt();
        b = in.nextInt();
        System.out.println(a + (b - a) * 2);
    }
}