diff --git a/algorithms/stack.md b/algorithms/stack.md
index 627ee2c6..063e3a64 100644
--- a/algorithms/stack.md
+++ b/algorithms/stack.md
@@ -6,3 +6,4 @@ Stack
 - Write an algorithm to determine if all of the delimiters in an expression are matched and closed.
   - E.g. `{ac[bb]}`, `[dklf(df(kl))d]{}` and `{[[[]]]}` are matched. But `{3234[fd` and `{df][d}` are not.
   - [Source](http://blog.gainlo.co/index.php/2016/09/30/uber-interview-question-delimiter-matching/)
+- Sort a stack in ascending order using an additional stack.