You are given two integers a and b (a ≤ b). How many prime numbers are there on the interval from a to b, inclusive?

Input

The input contains two integers a and b (2 ≤ a ≤ b ≤ 1 000 000), separated by a single space.

Output

Output a single integer — the number of primes between a and b, inclusive.

见题面 Input 部分

见题面 Output 部分