diff --git a/1/trebuchet.py b/1/trebuchet.py
index 9d5db6d..1012870 100644
--- a/1/trebuchet.py
+++ b/1/trebuchet.py
@@ -6,8 +6,10 @@ def calibrate(data: list) -> int:
     """
     Solve part a.
     """
-    n = "".join(c for c in data if c.isdigit())
-    return int(n[0] + n[-1])
+    # filter digits
+    digits = [c for c in data if c.isdigit()]
+    # return the sum of the first and the last digit
+    return int(digits[0] + digits[-1])
 
 
 def translate(s: str) -> str: