Multiplying cells together

I am trying to generate a standard formula to multiply 4 cells together. It is important to note that some of the cells will not have a number in them.
Eg Cell A1 = 10, Cell A2 = 5, Cell A3 = blank, Cell A4 = 2. The answer I am looking for is 100. However, when I try the following formula =sum(+A1*A2*A3*A4) it only gives 0 as an answer (because cell A3 is blank). Is there away to include cell A3 in the formula and get the correct answer?

Any help on this would be greatly appreciated

Thanks

=product(a1,a2,a3,a4)

or =product(A1:A4)

Works like a dream. Many thanks