Problem:
Score : 100 points

Problem Statement

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.

Sample Input 1

2 4 6

Sample Output 1

YES

Since 4-2 = 6-4, this arrangement of poles is beautiful.

Sample Input 2

2 5 6

Sample Output 2

NO

Since 5-2 \neq 6-5, this arrangement of poles is not beautiful.

Sample Input 3

3 2 1

Sample Output 3

YES

Since 1-2 = 2-3, this arrangement of poles is beautiful.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

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

class Main {

    public static void main(String[] args) throws Exception {

        try {

            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

            String[] pillarHeightList = br.readLine().split(" ");
            int firstPillar = Integer.parseInt(pillarHeightList[0]);
            int secondPillar = Integer.parseInt(pillarHeightList[1]);
            int thirdPillar = Integer.parseInt(pillarHeightList[2]);

            String isPillarsBeautiful = "NO";

            if ((secondPillar - firstPillar) == (thirdPillar - secondPillar)) {
                isPillarsBeautiful = "YES";
            }

            System.out.println(isPillarsBeautiful);

        } catch (IOException | NumberFormatException e) {
            e.printStackTrace();
            System.exit(0);
        } catch (final Exception e) {
            e.printStackTrace();
            System.exit(0);
        }
    }
}