WPF datagrid cell textbox change event

Entity/Class:

  public class FeesDetails : INotifyPropertyChanged  
   {  
     public int Id { get; set; }  
     public string FeesName { get; set;}  
     public string FeesDetailsName { get; set; }  
     public int? PaidAmount { get; set; }  
     public event PropertyChangedEventHandler PropertyChanged;  
     private void NotifyPropertyChanged(System.String info)  
     {  
       if (PropertyChanged != null)  
       {  
         PropertyChanged(this, new PropertyChangedEventArgs(info));  
       }  
     }  
     public int feesAmount { get; set; }  
     public int FeesAmount  
     {  
       get  
       {  
         return this.feesAmount;  
       }  
       set  
       {  
         if (value != this.feesAmount)  
         {  
           this.feesAmount = value;  
           NotifyPropertyChanged("FeesAmount");  
         }  
       }  
     }  
   }  

XAML:

  <DataGrid   
       AutoGenerateColumns="False"   
       Height="211" HorizontalAlignment="Left"   
       Margin="174,177,0,0" Name="setupFeesDataGrid"   
       VerticalAlignment="Top" Width="414"   
       CanUserAddRows="False">  
       <DataGrid.Columns>  
         <DataGridTextColumn Header="Fees Details Name" Binding="{Binding Path=FeesName}" Width="250"/>  
         <DataGridTemplateColumn Header="Fees Amount" Width="80">  
           <DataGridTemplateColumn.CellTemplate >  
             <DataTemplate >  
               <TextBox Name="feesAmountTextBox" TextChanged="feesAmountTextBox_TextChanged" Text="{Binding Path=FeesAmount,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" ></TextBox>  
             </DataTemplate>  
           </DataGridTemplateColumn.CellTemplate>  
         </DataGridTemplateColumn>  
       </DataGrid.Columns>  
     </DataGrid>  

CS code :

  private void feesAmountTextBox_TextChanged(object sender, TextChangedEventArgs e)  
     {  
       FeesDetails chalan = new FeesDetails();  
       chalan = setupFeesDataGrid.SelectedItem as FeesDetails;// get selected item  
       // Other i am summarizing grid cell value in a combobox  
       decimal TGBP = 0 ;  
       for (int i = 0; i < setupFeesDataGrid.Items.Count; i++)  
       {  
         FeesDetails obj = setupFeesDataGrid.Items[i] as FeesDetails;  
         TGBP += Convert.ToDecimal(obj.FeesAmount); // getting cell value   
       }  
       totalTextBox.Text = TGBP.ToString("F");   
     }