c# - Problem when summing selected cells in DataGridview -

i using code sum selected cells. work when user selecte cell letter throws exceptions : ) how can secure when in selectet cells letters dont make sum

private void datagridview1_databindingcomplete(object sender, datagridviewbindingcompleteeventargs e)      {          string filterstatus = datagridviewautofiltercolumnheadercell.getfilterstatus(datagridview1);          if (string.isnullorempty(filterstatus))          {              showalllabel.visible = false;              filterstatuslabel.visible = false;          }          else          {              int result = -1;             int32.tryparse(filterstatus, out result);             if (result != 0)             {                  // number                  showalllabel.visible = true;                   filterstatuslabel.visible = true;                   filterstatuslabel.text = filterstatus;              }             else             {                  // can number yet won't adding             }         }      }