Can't understand what python wants from me

[Oleksiy Khilkevich]

Hello, everyone,
This may be a totally noob question, but since I am one, so here is it.

I have the following code (not something much of): 
http://paste.debian.net/27204
The current code runs well, but the problem is with input value: 
http://paste.debian.net/27205
Аs you can see, the numbers are ok, but strings and characters cause 
"not defined" error.

I've obviously missing something important, but tutorial says nothing 
about this.

Thank you for your help.