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: Wrong Answer)

import java.io.*;
import java.lang.*;
import java.util.*;

class Main {
    public static void main(String[] args) {
      
        Scanner input = new Scanner(System.in);
        int A = input.nextInt();
        int B = input.nextInt();
        
        if(A == 0 || B == 0)
        {
            System.out.println("IMPOSSIBLE");
        }
        
        if(A > B)
        {
            for(int i=1; i<=A; i++)
            {
                int sumA = A-i;
                int sumB = B-i;
                if(sumB < 0)
                {
                    sumB*=-1;                    
                }
                if(sumA == sumB)
                    {
                        System.out.println(i);
                        break;
                        
                    }
                
                
            }
        }
        else 
        {
            for(int i=1; i<=B; i++)
            {
                int sumA = A-i;
                int sumB = B-i;
                if(sumA < 0)
                {
                    sumA*=-1;                    
                }
                if(sumA == sumB)
                    {
                        System.out.println(i);
                        break;
                        
                    }
                
                
            }
            
        }
        
        
    }
    
    
}