3978：Primes

A pretty straight forward task, calculate the number of primes between 2 integers.

Given 2 integers A ≤ B < 10⁵ what’s the number of primes in range from A to B inclusive.

Note: A prime number is a positive integer greater than 1 and is divisible by 1 and itself only. For N to be prime it is enough to test the divisibility of numbers less than or equal to square root of N.

As many as 1000 lines, each line contains 2 integers A and B separated by a space. Input is terminated when A = B = -1 (Do not process this line).

For every line in input – except for the last line where A = B = -1 - print the number of prime numbers between A and B inclusive.