Problem Statement

You are given positive integers N and M.
Find the smallest positive integer X that satisfies both of the conditions below, or print -1 if there is no such integer.

• X can be represented as the product of two integers a and b between 1 and N, inclusive. Here, a and b may be the same.
• X is at least M.

Input

The input is given from Standard Input in the following format:
N M

Output

Print the smallest positive integer X that satisfies both of the conditions, or -1 if there is no such integer.

Constraints

• $1\leq N\leq 10^{12}$
• $1\leq M\leq 10^{12}$
• N and M are integers.

Sample Input 1

5 7

Sample Output 1

8

First, 7 cannot be represented as the product of two integers between 1 and 5.
Second, 8 can be represented as the product of two integers between 1 and 5, such as $8=2\times 4$.
Thus, you should print 8.

Sample Input 2

2 5

Sample Output 2

-1

Since $1\times 1=1, 1\times 2=2, 2\times 1=2$, and $2\times 2=4, only 1, 2$, and 4 can be represented as the product of two integers between 1 and 2,
so no number greater than or equal to 5 can be represented as the product of two such integers.
Thus, you should print -1.

Sample Input 3

100000 10000000000

Sample Output 3

10000000000

For a=b=100000 (=10^5), the product of a and b is 10000000000 (=10^{10}), which is the answer.
Note that the answer may not fit into a 32-bit integer type.

见题面 Input 部分

见题面 Output 部分