# -*- coding: utf-8 -*-
# http://odz.sakura.ne.jp/projecteuler/index.php?cmd=read&page=Problem%2037
# 
# そのまま..
require 'prime'
def lprime?(x)
  x.each_index.reduce(true) {|ret, i|
    ret && Prime.prime?(x[0 .. i].join.to_i)
  }
end
def rprime?(x)
  x.each_index.reduce(true) {|ret, i|
    ret && Prime.prime?(x[(x.size - i - 1) .. -1].join.to_i)
  }
end
puts Prime.each(1000000).reduce(0) {|sum, prime|
  if (prime > 10)
    x = prime.to_s.chars.to_a
    sum + (lprime?(x) && rprime?(x) ? prime : 0)
  else
    sum
  end
}