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: Wrong Answer)

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner s = new Scanner(System.in);
		String str = s.next();
		String str1 = s.next();
		String ans = "";
		ans = ans + " ";
		int i = 0;

		// StringBuilder sb= new StringBuilder();
		for (i = 0; i < Math.max(str.length(), str1.length()) - 1; i++) {
			char cc = str.charAt(i);
			char cf = str1.charAt(i);

			ans = ans + cc + cf;
		}
		if (str.length() > str1.length()) {
			ans = ans + str1.charAt(i - 1);
		}
		if (str.length() < str1.length()) {
			ans = ans + str.charAt(i - 1);
		}
		System.out.println(ans);
	}

}