Contest: Task: Related: TaskB

Score: $100$ points

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.

- All values in input are integers.
- $0 \leq A,\ B \leq 10^9$
- $A$ and $B$ are distinct.

Input is given from Standard Input in the following format:

$A$ $B$

Print the integer $K$ satisfying the condition.

If such an integer does not exist, print `IMPOSSIBLE`

instead.

2 16

9

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

0 3

IMPOSSIBLE

No integer satisfies the condition.

998244353 99824435

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