The present invention provides a compound represented by formula (1): or pharmaceutically acceptable salt thereof, wherein X and Y are the same or different from each other and represent a hydrogen atom, a halogen atom, a C1-6 alkyl group, or a C1-6 alkoxy group, wherein the C1-6 alkoxy group may be substituted with a C1-6 alkoxy group, and Z and W are the same or different from each other and represent a hydrogen atom, a halogen atom, or a C1-6 alkyl group.