My kids tend to lose cards quite often but we still play some games.

For example: We have assembled quite a pile of cards and are playing a game in which all the cards are dealt out before playing.

We discovered:

If two people are playing-1 card will be left,
3 people-2 cards left,
4 people-3 cards left,
5 people- 4 cards left,
6 people-5 cards left,

and 7 people- 0 cards left

How many cards are in this deck?