Problem:
Score: 100 points

Problem Statement

We have two distinct integers A and B.

Print the integer K such that |A - K| = |B - K|.

If such an integer does not exist, print IMPOSSIBLE instead.

Constraints

All values in input are integers.

0 \leq A,\ B \leq 10^9

A and B are distinct.

Input

Input is given from Standard Input in the following format:

A B

Output

Print the integer K satisfying the condition.

If such an integer does not exist, print IMPOSSIBLE instead.

Sample Input 1

2 16

Sample Output 1

9

|2 - 9| = 7 and |16 - 9| = 7, so 9 satisfies the condition.

Sample Input 2

0 3

Sample Output 2

IMPOSSIBLE

No integer satisfies the condition.

Sample Input 3

998244353 99824435

Sample Output 3

549034394

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

import java.util.Scanner;
public class Main{
	static int getK(int a,int b) {  
		int i,k=0;
		  i=a+b;
		    k=i/2;
		  return k ;
  } 
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int a,b,i,k=1;
	Scanner scan=new Scanner(System.in);
	 a=scan.nextInt();
	 b=scan.nextInt();
    i=a+b;
    if(i%2==0) {
    System.out.println(getK(a,b));
   }
   else { 
   System.out.println("IMPOSSIBLE");
   }
	   }
	
	 }