Problem Statement

Find the price of a product before tax such that, when the consumption tax rate is $8$ percent and $10$ percent, the amount of consumption tax levied on it is $A$ yen and $B$ yen, respectively. (Yen is the currency of Japan.)

Here, the price before tax must be a positive integer, and the amount of consumption tax is rounded down to the nearest integer.

If multiple prices satisfy the condition, print the lowest such price; if no price satisfies the condition, print -1.

Constraints

• $1 \leq A \leq B \leq 100$
• $A$ and $B$ are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

If there is a price that satisfies the condition, print an integer representing the lowest such price; otherwise, print -1.