Opening a Confirmation modal window from httppost Action Method

Opening a Confirmation modal window from httppost Action Method

I have a parent screen named DataEntry.aspx with the input fields and
submit button. On clicking submit httppost DataEntry Action Method gets
called and some processing is done fetching some values. Based on that
values i need to show a Confirmation pop up with the options 'Continue and
Cancel' when user clicks on continue the control will move ahead with the
execution of DataEntry Post Method and move to the final page but when the
user clicks the cancel button he will stay on the DataEnry Page to ReEnter
the Data.
Any help would be appreciated m struggling with this issue for so long.