require "prime"
require "set"
prime_max = 5000000

gets
set = gets.split.map(&:to_i).to_set

ok = Set.new
start = 1
remain = set
exist_flag = false
complete_flag = false

Prime.each(prime_max) do |prime|
  nums = prime.to_s.each_char.map(&:to_i).to_set
  if set.superset?(nums)
    unless complete_flag
      exist_flag = true
      remain -= nums
      if remain.empty?
        complete_flag = true
      end
    end
  else
    if exist_flag
      if complete_flag
        ok << prime - 1 - start
      end
      remain = set
    end
    start = prime + 1
  end
end
if complete_flag
  ok << prime_max - start
end
if ok.empty?
  puts(-1)
else
  puts(ok.max)
end