In this task, you are given two sets, and you need to count the number of elements at the intersection of two given sets.  A Set is shown by two curly braces and comma-separated numbers inside, like {1, 2, 3}. The intersection of two given sets is the largest set which contains all the elements that are common to both sets. To find the intersection of two given sets, A and B is a set consisting of all the elements common to both A and B.

Let me give you an example: Set1: '{11, 4, 6}', Set2: '{2, 3, 4, 10, 11, 20}'. How many elements are there in the intersection of Set1 and Set2 ?
The answer to this example can be: 2
Here is why: Intersection of Set1 and Set2 is {11, 4} and it has 2 elements. So, the answer is 2.

OK. solve this:
Set1: '{9, 2, 17, 1}', Set2: '{1, 4, 5, 7, 9, 10, 13, 15, 18, 19}'. How many elements are there in the intersection of Set1 and Set2 ?
Answer:
2