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;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
	int a=sc.nextInt();
    int b=sc.nextInt();
    int c=sc.nextInt();
    int ab=b-a;
    int bc=c-b;
    if (ab==bc){
      System.out.println("YES");
    } else {
      System.out.println("NO");
    }
  }
}