VS 2010 Count the textbox

I have a txtbox named txtNoOfLot wherein you will input random number(example 4) then on the other txtbox named txtLot, you will input 1 random Lot number then click the insert button then another 1 random Lot number until you meet the 4 required lot number inputs. After which a msg box will prompt that you have successfully inserted 4 lot numbers.

sample ui;

http://i.imgur.com/uestTLu.png?1