Thanks Bob, Teethless mama.

However, both the formulae result in 3 for the following data:
a1 f
a1 g
b1 h
b1
c1
c1 p
d1
d1 p

whereas, it should show 0. (Because, no seat is free- each one is
occupied in some shift(s))

Thanks again... for your time.
~Animesh