# -*- coding: utf-8 -*-
# http://odz.sakura.ne.jp/projecteuler/index.php?cmd=read&page=Problem%2035
#
# そのまま..
#
require 'prime'

def circular_prime?(x)
  a = x.to_s.chars.to_a
  (1 ... a.size).reduce(true) do |ret, i|
    ret && Prime.prime?(a.rotate(i).join.to_i)
  end
end
puts Prime.each(1000000 - 1).reduce(0) {|count, prime|
  count + (circular_prime?(prime) ? 1 : 0)
}