C# .NET - Interface is a value type or reference type?

Is Interface a value type or reference type? As interface supports both structure and a class. Structure is a value type and class is a reference type. So under which category does an interface come? value type or a reference type? 

I have a class  with 2 member variables int and string.

class test
{
 int x=10;
stiring name="samuel";


}

 string is a ref type and it goes to heap. int is a value type where is it stored?