Blogspot posts doesn't allow to insert "input" tag in its posts directly by HTML Editor of posts. To do so you can follow the following steps
- Goto the Templete from Admin portal of your blog
- click on edit html & add JQuery.js (preferably which is hosted on google /JQueryUI.
- in your post add a div in which you will add your input contents.
- Now again in your templete html editor, write JQuery to handle event and adding the controls
for demo code you can view this article Insert input elements in blogspot's post