Which octets are used for the network address and for host addresses in Class A Class B Class C?

There are 4 octets in an IP address as shown below:
Octet1.Octet2.Octet3.Octet4
Every IP class has different allocation of network and host ID.
For class A, the network and host IDs' allocation is as follows:
Network.Host.Host.Host
For class B, the network and host IDs' allocation is as follows:
Network.Network.Host.Host
For class C, the network and host IDs' allocation is as follows:
Network.Network.Network.Host
You may go to the following link get more info on IP address classes and their IDs:
www.iphow.co.cc