diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index 57a5042b..556be918 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -40,6 +40,14 @@
         android:layout_weight="2"
         android:orientation="horizontal">
 
+        <Button
+            android:id="@+id/btn_factorial"
+            style="@style/MyButton"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:layout_weight="1"
+            android:text="!"/>
+
         <Button
             android:id="@+id/btn_percent"
             style="@style/MyButton"