There are two logs, one 12 meters long and the other 21 meters long. If they are to be cut into small pieces of the same length, and there is no surplus, how many meters is the longest of each small piece of logs?
有两根圆木，一根长12米，另一根长21米．要把它们截成同样长的小段，且没有剩余，每小段圆木最长多少米？
<result>3</result>