require 'prime'

class Calc0012
  MAX = 5000000

  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @n = args.shift.first.to_i
    @as = args.shift.map(&:to_i)
    @prime = Prime.instance
  end

  def run
    primes = @prime.each(MAX).to_a
    as = @as.map { |a| 1 << a }.inject(:|)
    s = primes.map { |p| p.to_s.split(//).map(&:to_i).map { |a| 1 << a }.inject(:|) }
    (0...s.size).each do |i|
      s[i] = nil if (s[i] & ~as) != 0
    end

    max_range = -1
    i = 0
    loop do
      i += 1 while !s[i] && i < s.size
      break if i == s.size

      t = i
      i += 1 while s[i] && i < s.size

      u = (t...i).map { |a| s[a] }.inject(:|)
      if u == as
        min = t == 0 ? 1 : primes[t - 1] + 1
        max = i == s.size ? MAX : primes[i] - 1
        range = max - min
        max_range = range if max_range < range
      end
    end

    max_range
  end
end

puts Calc0012.new(STDIN.readlines).run if __FILE__ == $0