Write a Python program that prints length of the longest
sequence in the file dna.txt given in FASTA format. 

For example if the file contains 

>human
ACCGT
>mouse
AGTTATATA
>cat
AGT
>dog
GTGTATA

then the output should be 

9

Your program should work for any number of sequences and not just the 
given example.

Submit a hardcopy in class on Sept 24th.