diff --git a/deadsunrise/calc.rb b/deadsunrise/calc.rb
new file mode 100644
index 0000000..94be4f7
--- /dev/null
+++ b/deadsunrise/calc.rb
@@ -0,0 +1,47 @@
+class Calc
+
+  def add(operation)
+    return 0 if operation == ''
+    @clean_operands = clean(operation)
+    calculate(@clean_operands)
+  end
+
+  private
+
+  def clean(operation)
+    operands = replace_delimiters(operation)
+    check_for_negative_operands?(operands)
+    reject_big(operands)
+    return operands
+  end
+
+
+  def replace_delimiters(operation)
+    delimiters = parse_delimiter(operation)
+    operands = operation.gsub(/\/\/.*\n/ , '')
+    delimiters.flatten.each { |d| operands.gsub!(d.to_s,',') }
+    operands.split(',').map! {|s| s.to_i }
+  end
+
+  def parse_delimiter(operation)
+    delimiters = ["\n"]
+    delimiters << operation.scan(/\[([^[]+)\]/)
+    delimiters << operation.scan(/\/\/(.)\n/)
+  end
+
+  def check_for_negative_operands?(operands)
+    negatives = operands.reject {|i| i >= 0  }
+    raise("negatives not allowed #{negatives.join(',')}") unless negatives.empty?
+  end
+
+
+  def reject_big(operands)
+    operands.reject! {|i| i > 1000}
+  end
+
+
+  def calculate(operands)
+    operands.reduce(:+)
+  end
+
+end
diff --git a/deadsunrise/calc_spec.rb b/deadsunrise/calc_spec.rb
new file mode 100644
index 0000000..f92985b
--- /dev/null
+++ b/deadsunrise/calc_spec.rb
@@ -0,0 +1,66 @@
+require 'calc'
+
+describe 'calc' do
+
+  describe 'add' do
+
+    before(:each) do
+      @calc = Calc.new
+    end
+
+    it "should return 0 with an empty arg" do
+      @calc.add("").should == 0
+    end
+
+    it "should return 1 with 1" do
+      @calc.add('1').should == 1
+    end
+
+    it "should return 3 with 1,2" do
+      @calc.add("1,2").should == 3
+    end
+
+    it "should sum 2 or more numbers" do
+      @calc.add("1,2,3").should == 6
+    end
+
+    it "should allow new lines between numbers" do
+      @calc.add("1,2,3").should == 6
+      @calc.add("1\n2,3").should == 6
+    end
+
+    it "should allow different delimiters" do
+      @calc.add("//;\n1").should == 1 
+      @calc.add("//:\n1:2").should == 3
+      @calc.add("//;\n1;2;3").should == 6
+
+    end
+
+    it "should rise an exception if numbers are negative" do
+      lambda {@calc.add("-2")}.should raise_error(RuntimeError, 'negatives not allowed -2')
+      lambda {@calc.add("1,-2,3")}.should raise_error(RuntimeError, 'negatives not allowed -2')
+      lambda {@calc.add("//;\n1;2;1,-2,-3")}.should raise_error(RuntimeError, 'negatives not allowed -2,-3')
+    end
+
+
+    it "should ignore numbers bigger than 1000" do
+      @calc.add("1,2000,2").should == 3
+    end
+
+    it "should allow delimiters longer than 1 char" do
+      @calc.add("//[***]\n1***2***3").should == 6
+    end
+
+    it "should allow multiple delimiters" do
+      @calc.add("//[*][%]\n1*2%3").should == 6
+    end
+
+    it "should allow multiple delimiters longer than 1char" do
+      @calc.add("//[,,,][;][;;]\n1,,,2;3").should == 6
+      @calc.add("//;[***]\n1,***2,3").should == 6
+    end
+
+
+  end
+
+end