Text box validate

Hello all,
I have a problem with textbox validate script. i want to check validation of textbox 3 time and after 3 wrong attempt automatically right answer will display in a message box.
Ex:
var n=getField("item2").value;
if(n !="lightning")
{
app.alert("Try again...",3)
}
else
{
app.alert("Correct... ",3);
}

this code working properly, but i want to check it 3 times and then answer(anything message) will appear.

thanks,