"""

Sieve of Eratosthenes

find the prime under threshold (default to 1000)

"""

import math

def sievePrime(n=1000):

lst = range(0, n + 1)

lst[1] = 0

thres = int(math.sqrt(n)) + 1

for i in xrange(2, thres):

if lst[i] == 0:

continue

for j in xrange(i * 2, len(lst), i):

if lst[j] != 0:

lst[j] = 0

return [i for i in lst if i != 0]

if __name__ == "__main__":

try:

n = int(raw_input("Enter a positive integer as threshold: "))

except ValueError:

print "Enter only a positive integer, n > 1"

print "default 1000"

print sievePrime(n)