Problem Statement

You are given integers L,R (L < R).
Snuke is looking for a pair of integers (x,y) that satisfy both of the conditions below.

• $L \leq x < y \leq R$
• $\gcd(x,y)=1$

Find the maximum possible value of (y-x) in a pair that satisfies the conditions.
It can be proved that at least one such pair exists under the Constraints.

Input

Input is given from Standard Input in the following format:
L R

Output

Print the answer.

Constraints

• $1 \leq L < R \leq 10^{18}$
• All values in input are integers.

Sample Input 1

2 4

Sample Output 1

1

For (x,y)=(2,4), we have $\gcd(x,y)=2,$ which violates the condition.
For (x,y)=(2,3), the conditions are satisfied. Here, the value of (y-x) is 1.
There is no such pair with a greater value of (y-x), so the answer is 1.

Sample Input 2

14 21

Sample Output 2

5

Sample Input 3

1 100

Sample Output 3

99

见题面 Input 部分

见题面 Output 部分