How to combine two IsNull condition in IF expression in Qlikview?

I have three column as A, B, C

I'm writing an expression for column D in Qlikview to find out whenever column B & C IsNull I need to replace the value of C in column D. Similarly Vice versa for the remaining columns.

Expression:

=if((IsNull(A) and IsNull(B)), C,if((IsNull(B) and IsNull(C)), A,.....)

But I'm not getting the values in my output.

Was there any issue in the above expression ?

Can someone help me on it .