diff --git a/backup/backup.sh b/backup/backup.sh
index 9c31851..389f322 100755
--- a/backup/backup.sh
+++ b/backup/backup.sh
@@ -1,4 +1,14 @@
-#!/bin/bash
+#!/usr/bin/env bash
+
+deleteOldest() {
+  line_num=0
+  while IFS=  read -r -d $'\0'; do
+      if [ $line_num == 1 ]; then
+        $(rm -rf ${REPLY})
+      fi
+      ((line_num++))
+  done < <(find -maxdepth 1 -type d -print0 | sort -z)
+}
 
 # array of available collection names
 col=(app_user awarding decoration rank squad user promotion player war)
@@ -10,6 +20,9 @@ do
     then
       mongoexport --db cc --collection $i --out $(date '+%Y-%m-%d')/collections/${i}.json;
       cp -R ../api/resource $(date '+%Y-%m-%d')/
+      if [ $(ls -l | grep -c ^d) -gt 5 ]; then
+        deleteOldest
+      fi
     else
       mongoimport --db cc --collection $i --drop --file ${1}/collections/${i}.json
       rm -rf ../api/resource