diff --git a/Algo/Courses/Chapter 6 - Lists (Exercises).md b/Algo/Courses/Chapter 6 - Lists (Exercises).md
index 4bc0b66..90f6d45 100644
--- a/Algo/Courses/Chapter 6 - Lists (Exercises).md	
+++ b/Algo/Courses/Chapter 6 - Lists (Exercises).md	
@@ -276,3 +276,8 @@ let rec flattten = function
 		| e2::t2 -> e2==flatten(2::t));;
 
 val flatten: 'a list list -> 'a list = <fun>
+```
+Complexity : $O(\sum_{\forall{l\in{(el::ll)}}}^{}1+length(l))$
+
+
+