diff --git a/4/cleanup.py b/4/cleanup.py
index d091b9e..acb0b64 100644
--- a/4/cleanup.py
+++ b/4/cleanup.py
@@ -3,6 +3,9 @@ from aocd import submit
 
 
 def find_overlaps(sets: list) -> int:
+    """
+    count the number of sets that overlap
+    """
     overlaps = [1 if set.intersection(*pair) else 0 for pair in sets]
     return sum(overlaps)