Acton

import math

def sieve(n):
    isPrime = [True] * n
    isPrime[0] = False; isPrime[1] = False
    for i in range(2, int(math.sqrt(float(n)))+1):
        if isPrime[i]:
            for k in range(i*i,n,i): isPrime[k] = False

    return isPrime

count : (list[bool]) -> int
def count(bs):
    res = 0
    for b in bs:
        if b: res += 1
    return res


def primesTo(n):
    res = []
    isPrime = sieve(n)
    for i in range(2, n):
        if isPrime[i]: res.append(i)
    return res


actor main(env):
    if (len(env.argv) >= 2) and env.argv[1].isdecimal():
        print(count(sieve(int(env.argv[1]))))
    else:
        print("Usage: sieve <positive integer>")
    env.exit(0)