How do I read the enterprise custom fields in C#?

Hello,

At the moment I am stuck trying to read out an enterprise custom field in an office Addin for Project.

I know I can read out the custom fields for tasks like this and I am also able to get the project name.

app = this.Application;

//Custom field of a task
wbs = app.ActiveCell.Task.Text1;

//Project name
projectName = app.ActiveProject.Name;

But I don't know how I can read an enterprise custom field. 
I am trying to get the red marked field from the screenshot

Thx for your help in advance