#!/usr/bin/env ruby

require 'set'
require 'zipf'

n = ARGV.pop.to_i

all = []
all_sets = []
ARGV.each { |file|
  fp = ReadFile.new file
  a = []
  s = Set.new
  while line = fp.gets
    a << line
    s << line
  end
  all << a
  all_sets << s
}

joint_set = all_sets.pop
all_sets.each { |set|
  joint_set &= set
}

joint_set.each { |i|
  puts i
}