Migrated from Lutece 751 The prime number

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Description

Aftering learning the definition of the prime number, he is wondering how many prime numbers there are in $[n,m]$.So he wants you to help to solve this problem.

Input

There are several test cases.For each test case, standard input contains a line with two numbers $n$ and $m$ ($1\leq n\leq m\leq 10^9$). The input ends with $n = m = 0$.

Output

For each test case, print the answer.

Samples

1 6
4 12
0 0

3
3

Resources

hutu