How to extract a value of a variable in Simulink?

I want to extract a value of a variable in an algebraic loop, if the certain criteria is fulfilled. For example I want X to be equal 300, if it is, i want it to take take this value and use in another place in simulation.

I tried to stop simulation if the criteria is fulfilled but then I cannot use the value of X anymore. With To Workspace Block, X is changing in time, so I can only extract the matrix X=[0 0 0 ... 300]

Is there a way for example to stop subsystem, but the rest of the simulation still runs. (when I used Stop Block whole simulation stopped).

Any idea how can i extract this last value of X?