diff --git a/.gitignore b/.gitignore
index 32858aad..eb36edd3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,7 @@
 
 # virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
 hs_err_pid*
+
+# IntelliJ IDEA
+.idea/
+*.iml
\ No newline at end of file
diff --git a/README.md b/README.md
index 5ba5aaeb..c4ada605 100644
--- a/README.md
+++ b/README.md
@@ -183,7 +183,7 @@ You will commit all your code on a daily basis, when you finish your practice.
 
 #####Practice:#####
 
-1. [OOP Exercises](http://www.ntu.edu.sg/home/ehchua/programming/java/J3f_OOPExercises.html)
+1. [OOP Exercises](https://www3.ntu.edu.sg/home/ehchua/programming/java/J3f_OOPExercises.html)
 2. Design a building like a house and provide a builder to build it.
 3. Design a hospital and provide classes to build it (builder, factories, etc).