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 C (GCC 9.2.1) (judge verdict: Accepted)

 #include<stdio.h>
 #include<stdlib.h>
 int main()
 {
     int a,b,j=0;
     scanf("%d%d",&a,&b);
     for(int i=0;i<=b||i<=a;i++)
     {
         if(abs(a-i)==abs(b-i)) {printf("%d",i); j=1;  break;}
     }
        if(j==0) printf("IMPOSSIBLE");
 }