Andrei's Family

An arithmetic sequence is a sequence in which the pairwise difference is constant. For example $1, 4, 7, 10$ is an arithmetic sequence in which every number increases by $3$.

Andrei has three kids: Jerry, Vincent, and his eldest son, Chungus. Unfortunately, Andrei has forgotten Chungus' age. Luckily, he remembers that the ages of his sons form an arithmetic sequence. Given the age of Jerry and Vincent, find Chungus' age.

Input Specification

• The first line contains $V$, the age of Vincent (the youngest child.)
• The second line contains $J$, the age of Jerry (the middle child.)

Output Specification

Output one integer: Chungus' age (the eldest child.)

Examples

Example 1

Input

12
15

Output

18

Example 2

Input

69
72

Output

75

Example 3

Input

1
10

Output

19

Example 4

Input

5
5

Output

5

Model Solution

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Let Chungus' age be $C$. Then we have the following sequence of ages:

$$V, J, C$$

From the problem statement, this sequence is guaranteed to be an arithmetic series. By the definition of an arithmetic series, the pairwise difference is constant. Furthermore, since we have two adjacent elements, we can compute the pairwise difference, which is $J - V$.

It follows that the desired value $C$ is equal to $J + J - V$.

v = int(input())
j = int(input())
print(j + j - v)