The Sieve of Eratosthenes is an elegant algorithm for finding all of the prime numbers up to some limit n. The basic idea is to first create a list of numbers from 2 to n. The first number is removed from the list, and announced as a prime number, and all multiples of this number up to n are removed from the list. This process continues until the list is empty.

For example, if we wished to find all the primes up to 10, the list would originally contain 2, 3, 4, 5, 6, 7, 8, 9, 10. The 2 is removed and announced to be prime. Then 4, 6, 8 and 10 are removed, since they are multiples of 2. That leaves 3, 5, 7, 9. Repeating the process, 3 is announced as prime and removed, and 9 is removed because it is a multiple of 3. That leaves 5 and 7. The algorithm continues by announcing that 5 is prime and removing it from the list. Finally, 7 is announced and removed, and were done.

Write a program that prompts a user for n and then uses the sieve algorithm to find all the primes less than or equal to n.