diff --git a/Step2/kimnahyun/src/main/Main.java b/Step2/kimnahyun/src/main/Main.java
new file mode 100644
index 0000000..c3eebf5
--- /dev/null
+++ b/Step2/kimnahyun/src/main/Main.java
@@ -0,0 +1,77 @@
+package main;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class Main {
+    public static void main(String[] args) {
+        Calculator cal = new Calculator();
+    }
+
+    public static class Calculator {
+        int add(int i, int j){
+            return i + j;
+        }
+
+        int subtract(int i, int j) {
+            return i - j;
+        }
+
+        int multiply(int i, int j) {
+            return i * j;
+        }
+
+        int divide(int i, int j) {
+            return i / j;
+        }
+
+    }
+
+    public static class StringCalculator {
+
+        public int add(String text) {
+            if (toBlank(text)) {
+                return 0;
+            }
+
+            return sum(toInts(split(text)));
+        }
+
+        private boolean toBlank(String text) {
+            return text == null || text.isEmpty();
+        }
+
+        private String[] split(String text) {
+            Matcher m = Pattern.compile("//(.)\n(.*)").matcher(text);
+            if (m.find()) {
+                String customDelimeter = m.group(1);
+                return m.group(2).split(customDelimeter);
+            }
+            return text.split(",|:");
+        }
+
+        private int[] toInts(String[] values) {
+            int[] numbers = new int[values.length];
+            for (int i = 0; i < values.length; i++) {
+                numbers[i] = toPositive(values[i]);
+            }
+            return numbers;
+        }
+
+        private int sum(int[] numbers) {
+            int sum = 0;
+            for (int num : numbers) {
+                sum += num;
+            }
+            return sum;
+        }
+
+        private int toPositive(String value) {
+            int number = Integer.parseInt(value);
+            if (number < 0) {
+                throw new RuntimeException();
+            }
+            return number;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Step2/kimnahyun/src/test/StringCalculator_Test.java b/Step2/kimnahyun/src/test/StringCalculator_Test.java
new file mode 100644
index 0000000..b421b8d
--- /dev/null
+++ b/Step2/kimnahyun/src/test/StringCalculator_Test.java
@@ -0,0 +1,41 @@
+package test;
+
+import main.Main;
+import org.junit.Before;
+import org.junit.Test;
+/*import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeEach;*/
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class StringCalculator_Test {
+    private Main.StringCalculator cal;
+
+    @Before
+    public void setup() {
+        cal = new Main.StringCalculator();
+        System.out.println("Before");
+    }
+    @Test
+    public void add_empty() {
+        assertEquals(0,cal.add(null));
+        assertEquals(0,cal.add(""));
+    }
+    @Test
+    public void add_string() {
+        assertEquals(3, cal.add("3"));
+    }
+    @Test
+    public void add_seperate() {
+        assertEquals(8,cal.add("6,2"));
+        assertEquals(9,cal.add("3,2:4"));
+    }
+    @Test
+    public void add_regx() {
+        assertEquals(8, cal.add("//;\n3;4;1"));
+    }
+    @Test(expected = RuntimeException.class)
+    public void add_minus() {
+        cal.add("-1,2,3");
+    }
+}
\ No newline at end of file