diff --git a/day25.py b/day25.py
index 3704133..2541cbc 100644
--- a/day25.py
+++ b/day25.py
@@ -15,15 +15,17 @@ def transform(key, subject_number, loop_size=1):
 def part1(test_mode=False):
     my_input = aoclib.getInputAsArray(day=DAY, return_type=int, test=test_mode)
 
-    loop_card = 0
+    loop_card = 1
     public_key_card = 1
-    while public_key_card != my_input[0]:
+    while pow(7, loop_card, 20201227) != my_input[0]:
         loop_card += 1
         public_key_card = transform(public_key_card, 7)
 
     public_key_door = my_input[1]
 
-    return transform(1, public_key_door, loop_card)
+    # as we start with a key of 1, it's just a matter of
+    # multiplying public_key_door with itself loop_card times ....
+    return pow(public_key_door, loop_card, 20201227)
 
 
 def part2(test_mode=False):