datagridview - sum

I have populated a datagridview control with decimal numbers as below.
It also has a last row as Total.

How do I sum the figures in each column to place into the appropriate cell for the final row i.e. Total row?
Thanks

country column1 column2 column3

Russia 24,987.524 543,711,654.890 5,554.875
UK 65,977.324 513,311,254.690 6,654.175
US 84,987.524 943,711,654.890 3,554.875
Total

You loop through the Rows and add the Value from the appropriate cell to a running total.