Sieve of Eratosthenes in Ruby

sieve.rb

print "Enter maximum number : "
n = gets.to_i

primes = (2..n).to_a

i = 0

while primes[i]**2 < primes.last
  prime = primes[i]
  primes = primes.select { |num| num == prime || num % prime != 0 }
  i += 1
end

primes.each do |number|
  puts number
end