n = gets
raise unless n =~ /^[0-9]+$/
n = n.to_i
raise unless 1 <= n && n <= 500000
a = gets
raise unless a =~ /^([0-9]+ )+[0-9]+$/
a = a.split.map(&:to_i)
raise unless a.size == n
a.each do |x|
  raise unless 1 <= x && x <= 1_000_000_000
end