diff --git a/README.md b/README.md
index d9ec3f8..56184c2 100644
--- a/README.md
+++ b/README.md
@@ -25,4 +25,4 @@ git add demo.py
 git commit --message "Solved the first challenge of the workintech :)"
 git push origin master
 ```
-
+## Tamamlandı 🎉
diff --git a/demo.py b/demo.py
index 4592eec..f362bbe 100644
--- a/demo.py
+++ b/demo.py
@@ -1,5 +1,9 @@
+"""Demo module: circle area calculation"""
 
+import math
 
 def circle_area(radius):
-    """Returns the area of the circle of given radius"""
-    pass  # YOUR CODE HERE
+    """Calculate the area of a circle given its radius."""
+    if radius < 0:
+        return 0
+    return math.pi * radius**2