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.InputStreamReader;
import java.util.Scanner;

public class Main {
    public void main() {
        Scanner sc = new Scanner(new InputStreamReader(System.in));

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();

        println((a + c) == 2 * b ? "YES" : "NO");
    }

    public void print(Object o) {
        System.out.print(o);
    }

    public void println(Object o) {
        System.out.println(o);
    }

    public static void main(String[] args) {
        new Main().main();
    }
}
