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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    int a,b;
    a=sc.nextInt();
    b=sc.nextInt();
    int n=0;
    if(a<b){
      for(int i=0;i<b;i++){
        if(i-a==b-i){
          n=i;
          break;
        }
      }
    }else{
      for(int i=0;i<a;i++){
        if(a-i==i-b){
          n=i;
          break;
        }
      }
    }
    if(n!=0){
      System.out.println(n);
    }else{
      System.out.println("IMPOSSIBLE");
    }
  }
}