Originally, there were 1 gram, 3 gram, 5 gram, and 7 gram weights. After one weight was removed, the weights of 9 grams and 12 grams could no longer be weighed with a balance. How many grams were removed (weight The code can only be placed on one side of the balance.)
原来有1克、3克、5克、7克的砝码各一个，去掉一个砝码后，用天平再也无法称出9克和12克的重量，去掉的是多少克的砝码(砝码只能放天平的一边．)
<result>5</result>