Excel double IF statement: How to write function correctly for calender?

I need to write a function that follows the instructions below:

In cell B6 enter an if() function that checks to see if the contents of the cell to its left is blank. If it is, then execute another if() function that checks cell $E$27 to see if it is B5. If it is, then make the cell, 1; If it is not make the cell a blank (“”). If A6 is not a blank then insert one more than the content of cell A6.

The best I could come up with is:

=IF(A6=0,IF($E$27=B5,1,""),A6+1)

But I get returned a #VALUE! error. What is the correct way to write this function?