Title Description

The Environmental Protection Bureau of Oasis City uses a special numbering system to manage trees. The number of each tree is a positive integer, and experts have found that when the sum of the numbers in the number is a prime number, the tree has a stronger carbon sequestration ability. We now need to count the number of trees that meet the requirements in a certain area of the forest region, $L, R$.

Input format

Two integers, $L$ and $R$, separated by spaces

Output format

An integer represents the answer

Example

10 20

5