diff --git a/putzen.sh b/putzen.sh
index d165ec1..59ea62a 100644
--- a/putzen.sh
+++ b/putzen.sh
@@ -1,11 +1,9 @@
 #!/bin/sh
 
-if [ -z "$1" ]; then
-    echo "Usage: $0 [1-4]"
-    exit 1
-fi
+# Week number since 1970 modulo 4
+week=$(expr $(date +%s) / 604800 % 4)
 
-case $1 in
+case $week in
     1)
         /usr/bin/docker exec lab-signal-bot-lab-bot-1 \
             python create_task.py "LeineLab putzen" 2 "in 7 days" \