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: '{3, 4, 11, 12, 13, 16, 18, 19, 20}', Set2: '{4, 9, 12, 13, 20}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
4


question:
Set1: '{17}', Set2: '{10}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
0


question:
Set1: '{9, 18, 14}', Set2: '{16, 15}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:

0