You are playing a online RPG game with 9 friends of yours (10 people in total) and in the game there is a 2 players dungeon where you level up every time you enter and complete it and only two people get inside at most. At the beginning of the game everybody is level 1 as usual. Before the game release there was beta and you know how to level up fast from it, but there are some tricks you discovered:

- You cannot complete the dungeon alone.
- After completing this 2-players dungeon with your friend, you and your friend will get 1 level.
- If you play the dungeon with someone, one level below than you, you will get extra item since you help your friend to level up somehow.
- But you cannot enter the dungeon with more than one level below friend.
- Lastly, if you try to enter the dungeon with the same person again, no one will get any experience to level up or item.
- You can share the items later, they are not soulbound!

so 

> What is the maximum number of extra items you will get in total as a group from this dungeon?