There are 1 gram, 2 gram, 4 gram, and 8 gram weights, and one of them is lost. As a result, the weights of 7 grams and 12 grams cannot be weighed. How many grams are the lost weights?
有1克、2克、4克和8克的砝码各一个，丢了其中的一个，结果无法称出7克和12克的重量，丢了的砝码是多少克．
<result>4</result>