100 atcoder#ABC144A. [ABC144A] 9x9

[ABC144A] 9x9

Score : 100100 points

Problem Statement

Having learned the multiplication table, Takahashi can multiply two integers between 11 and 99 (inclusive) together. He cannot do any other calculation.

Given are two integers AA and BB.

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

Constraints

  • 1A201 \leq A \leq 20
  • 1B201 \leq B \leq 20
  • All values in input are integers.

Input

Input is given from Standard Input in the following format:

AA BB

Output

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

2 5
10

2×5=102 \times 5 = 10.

5 10
-1

5×10=505\times 10 = 50, but Takahashi cannot do this calculation, so print -1 instead.

9 9
81