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Write a method called retainAll that takes two sets of integers as parameters and that removes any values in the first set that are not found in the second set. 

For example, given sets: 

s1: [0, 19, 8, 9, 12, 13, 14, 15]  

s2: [0, 19, 2, 4, 5, 9, 10, 11]  

If the following call is made: 

retainAll(s1, s2);  

after the call, the sets would store the following values: 

s1: [0, 19, 9]  

s2: [0, 19, 2, 4, 5, 9, 10, 11]  

You are implementing a two-argument alternative to the standard Set method called retainAll, so you are not allowed to call that method to solve this problem. 

You are also not allowed to construct any structured objects to solve the problem (no set, list, stack, queue, string, etc) although you can construct iterators. 

Your method should not change the second set passed as a parameter.