One notation for describing a network range lists an address on the network followed by a forward slash and the number of bits in the address that describe the network. For a Class A network, the network designation would look like 10.0.0.0/8. For a Class B network, the network designation would look like 172.20.0.0/16. And for a Class C, it would like 192.168.50.0/24.
As a side note, in situations where network notation is required and a single address is not allowed, the notation can still be used to specify a single address. Use the notation 192.168.50.100/32. This specifies that all 32 bits of the address form the network. This is not relevant to the firewall generated by this program, but is a useful tidbit of information.