diff --git a/putzen.sh b/putzen.sh
index a5554b0..55abd35 100644
--- a/putzen.sh
+++ b/putzen.sh
@@ -1,7 +1,12 @@
 #!/bin/sh
 
-# Week number since 1970 modulo 4
-week=$(expr $(date +%s) / 604800 % 4)
+if [ -z "$1" ]; then
+    # Week number since 1970 modulo 4
+    week=$(expr $(date +%s) / 604800 % 4)
+else
+    week=$1
+fi
+
 
 case $week in
     0)