There are 1 gram, 2 gram, 4 gram and 8 gram weights. Now a weight is lost, so the weight of 12 grams and 7 grams cannot be weighed, how many grams of weight are lost.
有1克、2克、4克和8克的砝码各一个．现在丢了一个砝码，所以无法称出12克和7克的重量，丢掉的是多少克的砝码．
<result>4</result>