Excel 2007 : Complex IF Statements

Hi, right, i need a complex IF statement which counts up a column, and if the field in the column is blank, it says "Free Seat" into the cell. The probelm is, i cant get any part of the IF statement to work, i dont know where the if statement goes(in the cell of at the bottom of row 23). This is for my A levels, so if anyone casn help in anyway, thank you.

Basically, i am trying to make the IF statement look a LITTLE bit like this:

=IF(R4, "", Free)

Now thats obviously not right. Now the bigger problem is, i need to create a formula for the IF statement.. 54x bigger. Like this..

=IF(R4, "", Free+IF(R5, "", Free+IF(R6, "", Free+IF(R7, "", Free+IF(R8, "", Free............+IF(R54, "", Free)))))))))))))))))))))))))))))))))))))))))))))))))))))

If !anyone! can help me with this equation.. its a miracle.

Thank You Very Much!