instruction:
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.
question:
Set1: '{4, 8, 9, 12, 16, 17, 18, 19, 20}', Set2: '{1, 19, 20}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
2


question:
Set1: '{2, 4, 5, 11, 14, 17, 18, 19, 20}', Set2: '{3, 4, 8, 10, 11, 18}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
3


question:
Set1: '{17}', Set2: '{3, 9, 10, 11, 14, 16, 19}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:

0