Text Value - Add Contents Of Each Textbox And Show Result In Another Textbox

I am doing a lottery project in which i have 10 textbox and i want to add contents of each textbox and show result in another textbox say 11th textbox.

I am having the fallowing codes below on jsp page.

I want to add contents of textbox from(n50,n51.....n59) and show result in another textbox named (n60)

My question is that the valus stored in textbox is numeric and when i enter the value in any two of the textbox say named (n50 and n51) then the addition of its value must be seen in the result textbox say (n60) here. it does not wait for another textbox value which is left blank. the result of addition should be displayed simelteneously as i enter the value in text box.