I am using the `exam` class.

I am writing an exam, and I want the last footer (the final, last one to appear) to be "End of exam". 

I have this: 

```latex
    \pagestyle{headandfoot}
    \runningheadrule
    \firstpageheader{AP Calculus Practice Exam A1}{ Mao Laoshi }{Senior 2}
    \firstpageheadrule
    \runningheader{AP Calculus Practice Exam A1}
    { Page \thepage\ of \numpages}
    {Senior 2 }

    \footer{}
    {\iflastpage{End of exam}{Please go on to the next page\ldots}}
    {}

```