A company gets 16 cans of paint each and every month. The problem is that one of the 16 cans is always contaminated with lead. Fortunately, the company has the capacity to test for lead. But, because of time and money constraints, the results of the tests can't be made known until after all of the tests have been performed. Determine the fewest number of cans which should be tested in order to know for certain which of the 16 cans is contaminated.