Sum of datagridview column in a textbox based on another column distinct value in c#.net windows app

int Manpowercount= table
    .Select(r => r.Field<int>("ManPower"))      
    .Distinct()
    .Count();

var result = dataGridView1.Rows.Cast<DataGridViewRow>()
    .Where(r => r.Cells[0].Value != null)
    .Select (r => r.Cells[0].Value)
    .GroupBy(id => id)
        .OrderByDescending(id => id.Count()) 
        .Select(g => new { Id = g.Key, Count = g.Count() });