Having learned the multiplication table, Takahashi can multiply two integers between 1 and 9 (inclusive) together. He cannot do any other calculation.

Given are two integers A and B.

If Takahashi can calculate $A \times B$, print the result; if he cannot, print -1 instead.

Constraints

• $1 \leq A \leq 20$
• $1 \leq B \leq 20$
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

If Takahashi can calculate $A \times B$, print the result; if he cannot, print -1.

Examples

Input

2 5

Output

10

Input

5 10

Output

-1

Input

9 9

Output

81

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