Help to condense a formula

[Guest]

Is there a better way to express the following formula?
I'm in the process of upgrading an old spreadsheet and will have to increase
the future range in a more efficient manner than stated, but am having
trouble!

=IF(AND(ISNUMBER(Y679),ISNUMBER(Y680),ISNUMBER(Y681),ISNUMBER(Y682),ISNUMBER(Y683),ISNUMBER(Y684),ISNUMBER(Y685),ISNUMBER(Y686),ISNUMBER(Y687),ISNUMBER(Y688)),Y679+Y680+Y681+Y682+Y683+Y684+Y685+Y686+Y687+Y688,"not available")

TIA

 

[N Harkawat]

=if(count(y679:y688)=10,sum(y679:y688),"not available")