Problem Statement

Takahashi's cake has been eaten by someone. There are three suspects: person 1, person 2, and person 3.
There are two witnesses, Ringo and Snuke. Ringo remembers that person A is not the culprit, and Snuke remembers that person B is not the culprit.
Determine if the culprit can be uniquely identified based on the memories of the two witnesses. If the culprit can be identified, print the person's number.

Input

The input is given from Standard Input in the following format:
A B

Output

If the culprit can be uniquely identified based on the memories of the two witnesses, print the person's number; otherwise, print -1.

Constraints

• $1 \leq A, B \leq 3$
• All input values are integers.

Sample Input 1

1 2

Sample Output 1

3

From the memories of the two witnesses, it can be determined that person 3 is the culprit.

Sample Input 2

1 1

Sample Output 2

-1

From the memories of the two witnesses, it cannot be determined whether person 2 or person 3 is the culprit. Therefore, print -1.

Sample Input 3

3 1

Sample Output 3

2

见题面 Input 部分

见题面 Output 部分