Presents for a whole year

In the english christmas carol Twelve Days of Christmas, a lot of presents are distributed:

• on the first day there is one gift;
• on the second day, there are two new gifts and the same as on the previous day;
• on the third day, you receive three new gifts, plus two from the previous day and one from the day before that.

And so it goes on until the twelfth day. It’s easy to lose track of everything! How many gifts are there in total? The exhibit helps you to determine the exact number.