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.*;
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
 
     String[] nyu=sc.nextLine().split(" ");

//     String nyu=sc.nextLine();
int A=Integer.parseInt(nyu[0]);
int B=Integer.parseInt(nyu[1]);
int C=Integer.parseInt(nyu[2]);
//int D=Integer.parseInt(nyu);



//StringBuffer sb = new StringBuffer(nyu);
//		String dst = sb.reverse().toString();

//     String nyu2=sc.nextLine();
//int E=Integer.parseInt(nyu2);



//double A=Double.parseDouble(nyu[0]);
//double B=Double.parseDouble(nyu[1]);
/*
switch(C){
case 7:
case 5:
case 3:
System.out.println("YES") ;
break;
default:
System.out.println("NO") ;

break;
}
*/

//int res=Math.min((A*B),C);

//for(String tem:nyu){
//if(tem.equals("1"))res++;
//}
//int res=0;
//for(int i=0;i<300;i++){
//if(num[i]==1)res=i;
//}

//char[] c = nyu.toCharArray();


//System.out.println(nyu+"-"+line_r_2+"-"+nyu2+"-"+line_r_1);



if(B-A==C-B){
//double res=Math.ceil((AB)/2);

System.out.println("YES");
//}else if((C-B)<A){
//System.out.println("safe");

}else{
System.out.println("NO");

}




	}
}