diff --git a/calculator/Calculator.java b/calculator/Calculator.java
index 20ea080..dd7b339 100644
--- a/calculator/Calculator.java
+++ b/calculator/Calculator.java
@@ -1,15 +1,18 @@
-class Calculator{
+class Calculator {
 
-    public int addition(int num1,int num2){
-        return num1+num2;
+    public int addition(int num1, int num2) {
+        return num1 + num2;
     }
 
-    public int substraction(int num1,int num2){
-        return num1-num2;
+    public int subtraction(int num1, int num2) {
+        return num1 - num2;
     }
 
-    public int multiplication(int num1,int num2){
-        return num1*num2;
-    
+    public int multiplication(int num1, int num2) {
+        return num1 * num2;
+    }
 
-}
\ No newline at end of file
+    public int changeSign(int num) {
+        return -num;
+    }
+}