what's the precision for the output?
in the text it is written to be 10^-6 but in the sample output it is
10^-7
and
what happens if you don't use the underground,do you write 0 for the
number of stations or you don't write anything at all(just the time)

thanks for the answer everybody

My program writes 7 digits after the decimal point and gets AC.

>>what happens if you don't use the underground,do you write 0 for
the
>>number of stations or you don't write anything at all(just the
time)

Yes

> My program writes 7 digits after the decimal point and gets AC.
>
> >>what happens if you don't use the underground,do you write 0 for
> the
> >>number of stations or you don't write anything at all(just the
> time)
>
> Yes

I don't quite understand ...
If you don't use the underground the number of stations is 0 and you
just write the time and 0.
The time will be distance(start,end)/speed_by_foot

What isn't clear about this case ?