kangaroo.rb

def capitalize_even_(word)
 word.downcase
 word.gsub /..?/, '3'
end

def capitalize_third(word)
  word_array = word.split("")
  word_array.map.with_index do |i, index|
    if (index + 1) % 3 == 0
      word_array[index].upcase
    else
      word_array[index]
    end
  end.join
end

p capitalize_third('kangaroo')