Three if statements to calculate number of days lapsed

I have two dates fields, BEGIN DATE and END DATE, and I want to capture the number of days between these two dates. The fields may also be blank. How do I create three if statements on one cell?
1) if BEGIN = 0, then show "N/A"
2) if BEGIN > 0 and END = 0, then show "N/A"
3) if BEGIN > 0 and END > 0, then show the number of days BEGIN - END

Can someone pls help me?

I copied and pasted this into my spreadsheet and am receiving an error "you've entered too few arguments for this function"... any ideas?

see attached

Perfect! That did it. Thank you!