An apparatus includes: an obtaining unit to obtain a plurality of addresses in order, and a storage unit to store a first group of addresses included in the plurality of addresses and obtained before a certain address is obtained by the obtaining unit, and to store a second group of addresses included in the plurality of addresses and obtained after the certain address is obtained by the obtaining unit. An extracting unit extracts one or more addresses from the first group of addresses when the obtaining unit further obtains an address that matches any address of the first group of addresses, or extracts one or more addresses of the second group of addresses when the obtaining unit further obtains an address that matches any address of the second group of addresses, wherein the one or more extracted addresses are other than the matched address.