from functools import reduce
from operator import mul
d = [int(x) for x in ''.join(line.strip() for line in open('pe8.txt'))]
dL = len(d)

L = int(input('Enter a set length (0 > L > '+str(dL)+')? '))
print ('Greatest product of', L, 'consecutive digits = ', end='')
print ("None." if L>dL else \
    max(reduce(mul, d[i:i+L]) for i in range(dL-L+1)))