You can use subnetmask based on IP range you have purchased. Here are the details.

IPv4 INSTALLATION ASSISTANCEThe first two IPs (network & gateway) and the last IP (broadcast) in your assignment are unusable for you.

/28 (13 usable) NETMASK = 255.255.255.240
/27 (29 usable) NETMASK = 255.255.255.224
/26 (61 usable) NETMASK = 255.255.255.192
/25 (125 usable) NETMASK = 255.255.255.128
/24 (253 usable) NETMASK = 255.255.255.0