Codeforces#285 Div2-B

285-div2-b.rb

# http://codeforces.com/contest/501/problem/B
q = gets.chomp.to_i
queries = []
q.times { queries << gets.chomp.split }

hash = Hash.new { |h, k| h[k] = [] }
queries.each do |old_name, new_name|
  root = hash.keys.select { |key| hash[key].last == old_name }.first
  if root.nil?
    hash[old_name] << new_name
  else
    hash[root] << new_name
  end
end

puts hash.keys.length
hash.keys.each { |key| puts "#{key} #{hash[key].last}" }