C# Datagridview sum of each group

Hi all,

i have a datagridview with two columns (Group& Qty).

            int _total = 0;
            for (int c = 0; c < GridView1.Columns.Count; ++c)
            {

                for (int i = 0; i < GridView1.Rows.Count; ++i)
                {

                    _total += Convert.ToInt32(GridView1.Rows[i].Cells["QTY"].Value);

                }
            }


//I don't know how to combine both Column and Row loops :S

I would like to have the sum of each group.  

GroupQty

A12
B14
C22
A9
C17
B1
A3

I have to get a return (MessageBox for example):
A= 24
B=15
C =39

Thank you,

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