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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class Main {
	public static void main(String[] args) throws IOException{


		// 読み込み
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String line;
		String[] temp;

		line=br.readLine();
		temp=line.split(" ");

		int a = Integer.valueOf(temp[0]);
		int b = Integer.valueOf(temp[1]);
		int c = Integer.valueOf(temp[2]);


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

	}
}
