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

import java.util.Scanner;

public class Main {
	public static void main(String... args) {
		Scanner in = new Scanner(System.in);

		int a, b, c;

		a = in.nextInt();
		b = in.nextInt();
		c = in.nextInt();

		if(b - a == c - b) {
			System.out.println("YES");
		} else {
			System.out.println("NO");
		}
	}
}
