题目描述
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
输入格式
见题面
输出格式
见题面
样例输入
2 5 6
样例输出
NO