A rectangular wooden board with a length of 45 cm and a width of 20 cm is sawed into several squares without any residue. What is the longest side length of the sawn square?
一块长45厘米，宽20厘米的长方形木板，把它锯成若干块正方形而无剩余，所锯成的正方形边长最长是多少厘米？
<result>5</result>