I have a problem that i need to monitor centos 7 available memory As you can see below

As I calulate then it isn't 68% as opmanager shows below

but it is what top % shows below

But opmanager shows the same thing that htop shows as you can see below:

But the thing is that htop or opmanager doesn't show precisely the memory utilization.

How can i monitor command free -m Available mem with snmp?

Here is also the output of cat proc/meminfo