As you can read in music lyrics we have this case:
You receive in the first day:
A Partridge in a Pear Tree
In the second day you receive:
Two Turtle Doves and A Partridge in a Pear Tree
In the third day you receive:
Three French Hens, Two Turtle Doves and A Partridge in a Pear Tree
And so on until the twelfth day (look the image above the presents).
After these twelve days you will receive how many presents from your true love?
Image Source: Wikipedia