I'm a python programmer and I genrally happens that some problem on CF does not have any submission in Python, it is either Python 2 or Python 3 but ...

This problem that needs simple dfs ( sorry for spoiler but right now I'm not asking for help in solution ) gives Run Time Error on test 15.

After failing to get several times on this problem , I went for the accepted submissions then I found most of them having same result as mine ( Run Time Error on test 15 ) and there is no Accepted solutions in Python.

I'm here to ask may someone correct or find the error why it is getting RE or tell me the exact reason.

My code

Although this problem is from Educational Round 1.

I don't know at that time CF allows submissions in python or not. Somehow I managed to get AC using C++.

Sorry for my poor english. Thank You.