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 Java7 (OpenJDK 1.7.0) (judge verdict: Time Limit Exceeded)


import java.util.Scanner;
import java.lang.Long;
public class Main {

	public static void main(String[] args)
	{
		Scanner sc= new Scanner(System.in);
	     
		long A = sc.nextInt();
		long B = sc.nextInt();
		
		int i=0;
		for(int a = 1;a<Long.MAX_VALUE;++a)
		{
		if(Math.abs(A-a)==Math.abs(B-a))
		{
			i = a;
			break;
		}
		}

		if(i>0)
		{
			System.out.println(i);
		}
		else
			System.out.println("IMPOSSIBLE");
	}
	}