Adding a column of numbers

Hello, I have a file, and one column has both positive and negative numbers. Does anyone know how I can calculate the total of all the values (i.e, +ve and -ve).
eg:
col1 col2 col3
data 23 data
data 76 data
data -30 data

Thanks
Khoom

>cat cols
data 23 data
data 76 data
data -30 data

awk -F" " 'BEGIN {x=0} {x+=$2} END {print x}' cols