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.*;

public class Main{



	public static void main(String[] args) {
		
		int input;
		ArrayList<Integer> tempList;
		tempList = new ArrayList<Integer>();

		Scanner s = new Scanner(System.in);

		for (int i=0; i<3; i++){
			input = s.nextInt();
			tempList.add(input);
		}

		Collections.sort(tempList);

		int a,b,c;

		a = tempList.get(0);
		b = tempList.get(1);
		c = tempList.get(2);

		if ((b-a) == (c-b)){

			System.out.println("YES");

		}
		else{
			System.out.println("NO");
		}

	}

}