Substracting numbers in non contigous cells

Hi!
I need a formula to substract numbers in non contigous cells THAT ARE
IN ONE COLUMN and have the result in other cell, for example:


..=2E.....................A...................B

R1..................................BLANKCELL
R2..................................BLANKCELL
R3..................................15
R4..................................BLANKCELL
R5..................................BLANKCELL
R6..................60.............75
R8..................................BLANKCELL
R9..................................BLANKCELL
R10................................BLANKCELL
R11................................BLANKCELL
R12................................BLANKCELL
R13................................BLANKCELL
R14..............175.............250
R15................................BLANK
R16................................BLANK
R17................................BLANK
R18................................BLANK
R19..............50...............300


Any help will be appreciated

Thanks and regards

Guillermo Padr=F3n

B1==IF(ISBLANK(A1),"",SUM($A$1:A1))
and copy formula drop down

Ok.
IŽll try it.
Thanks a lot!
I appreciate your time and help
Best regards