p03759 AtCoder Beginner Contest 058 - ι⊥l
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.

Examples

Input

2 4 6


Output

YES


Input

2 5 6


Output

NO


Input

3 2 1


Output

YES
```python
a,b,c=map(int,input().split());print(" YNEOS"[b-a==c-b::2]) 
```