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.

-----Sample Input-----
2 5

-----Sample Output-----
10

$2 \times 5 = 10$.

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