diff --git a/13/13.py b/13/13.py
new file mode 100644
index 0000000..2eaded5
--- /dev/null
+++ b/13/13.py
@@ -0,0 +1,14 @@
+
+with open("input") as f:
+    t, buses = f.read().strip().split("\n")
+    t = int(t)
+    buses = buses.split(',')
+
+first = map(int, filter(lambda x: x!='x', buses))
+a, b = min((x-t%x, x) for x in first)
+print(a*b)
+
+# https://en.wikipedia.org/wiki/Chinese_remainder_theorem
+
+
+
diff --git a/13/input b/13/input
new file mode 100644
index 0000000..6a5ab7a
--- /dev/null
+++ b/13/input
@@ -0,0 +1,2 @@
+1004345
+41,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,37,x,x,x,x,x,379,x,x,x,x,x,x,x,23,x,x,x,x,13,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,29,x,557,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,19