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Contest: Task: Related: TaskB

Score : $100$ points

### Problem Statement

Three poles stand evenly spaced along a line. Their heights are $a$, $b$ and $c$ meters, from left to right. We will call the arrangement of the poles beautiful if the tops of the poles lie on the same line, that is, $b-a = c-b$.

Determine whether the arrangement of the poles is beautiful.

### Constraints

• $1 \leq a,b,c \leq 100$
• $a$, $b$ and $c$ are integers.

### Input

Input is given from Standard Input in the following format:

$a$ $b$ $c$


### Output

Print YES if the arrangement of the poles is beautiful; print NO otherwise.

### Sample Input 1

2 4 6


### Sample Output 1

YES


Since $4-2 = 6-4$, this arrangement of poles is beautiful.

### Sample Input 2

2 5 6


### Sample Output 2

NO


Since $5-2 \neq 6-5$, this arrangement of poles is not beautiful.

### Sample Input 3

3 2 1


### Sample Output 3

YES


Since $1-2 = 2-3$, this arrangement of poles is beautiful.