diff --git a/lib/sg_romanizer.rb b/lib/sg_romanizer.rb
index 9ab2218..002fc7a 100644
--- a/lib/sg_romanizer.rb
+++ b/lib/sg_romanizer.rb
@@ -1,9 +1,64 @@
 class SgRomanizer
   def romanize(arabic)
-    # write your code here
+    level4_num, level3_num, level2_num, level1_num = arabic.to_s.rjust(4).split('').map(&:to_i)
+    level1 =
+      case level1_num
+      when (1..3) then 'I' * level1_num
+      when 4 then 'IV'
+      when 5 then 'V'
+      when (6..8) then 'V' + 'I' * (level1_num - 5)
+      when 9 then 'IX'
+      else
+        ''
+      end
+    level2 =
+      case level2_num
+      when (1..3) then 'X' * level2_num
+      when 4 then 'XL'
+      when 5 then 'L'
+      when (6..8) then 'L' + 'X' * (level2_num - 5)
+      when 9 then 'XC'
+      when 10 then 'C'
+      else
+        ''
+      end
+    level3 =
+      case level3_num
+      when (1..3) then 'C' * level3_num
+      when 4 then 'CD'
+      when 5 then 'D'
+      when (6..8) then 'D' + 'C' * (level3_num - 5)
+      when 9 then 'CM'
+      when 10 then 'M'
+      else
+        ''
+      end
+    level4 =
+      case level4_num
+      when (1..3) then 'M' * level4_num
+      else
+        ''
+      end
+    "#{level4}#{level3}#{level2}#{level1}"
   end
 
   def deromanize(roman)
-    # write your code here
+    table = [
+      %w(I II III IV V VI VII VIII IX),
+      %w(X XX XXX XL L LX LXX LXXX XC),
+      %w(C CC CCC CD D DC DCC DCCC CM),
+      %w(M MM MMM),
+    ]
+
+    remain_roman = roman
+    table.reverse.map do |row|
+      x = row.reverse.filter { remain_roman.match(/^#{_1}/) }.first
+      if x
+        remain_roman = remain_roman.sub(x, '')
+        row.find_index(x) + 1
+      else
+        '0'
+      end
+    end.join.to_i
   end
 end