#encoding:utf-8 No.0511 2014.11.10
n = 30
ary = Array.new(n,"no")
(n-2).times do
  i = gets.chomp.to_i
  ary[i-1] = "yes"
end

ary.each_with_index do |item,idx|
  if item != "yes"
    puts idx + 1
  end
end