Go: package main

import (
        "fmt"
)

const MAX int = 1000000
var primes [MAX]int

func main() {
        Init()
        var n, cnt int
        for {
                _, err := fmt.Scanf("%d", &n)
                if err != nil {
                        break
                }
                cnt = 0
                for i := 2; i <= n; i++ {
                        cnt += primes[i]
                }
                fmt.Printf("%d\n", cnt)
        }
}

func Init() {
        for i := 0; i < MAX; i++ {
                primes[i] = i
        }

        Soe()

        for i := 0; i < MAX; i++ {
                primes[i] %= 2
        }
        primes[1] = 0
        primes[2] = 1
}

func Soe() {
        for i := 2; i < MAX; i++ {
                if primes[i] > 0 {
                        for j := 2; j < MAX/i; j++ {
                                if i * j < MAX {
                                        primes[i*j] = 0
                                }
                        }
                }
        }
}

Python: import math
  
def yo(n):
    if n==1:    return False
    s=2
    while s <= int(math.sqrt(n)):
        if n%s == 0:    return False
        s+=1
    return True
  
while True:
    c=0
    try:
        for i in range(1, int(input(">>"))+1,2):
            if yo(i)==True:    c+=1
        print(c)
    except:
        break

Python: import math

num_max = 999999
i = 3
prime_list = [2]
while i<num_max :
	judge = True
	j = 0
	while prime_list[j] <= math.sqrt(i) :
		if (i%prime_list[j]==0) :
			judge = False
			break
		j += 1
	if(judge) :
		prime_list.append(i)
	i += 2
while True :
    try:
        n = input()
        k = 0
        while prime_list[k] <=  n :
            k += 1
        print(k)
    except EOFError :
        break

Python: def era(x,p):
  if x<=p or (x>p and x%p!=0):
    return x
  else:
    return None
def eratosthenes(n):
  A=[i for i in range(2,n+1)]
  p=2
  while p<=n**(1/2):
    A=list(filter(lambda x:era(x,p),A))
    p+=1
  return(A)

inputs=[]
while True:
  try:
    inputs.append(int(input()))
  except EOFError:
    break

for i in inputs:
  print(len(eratosthenes(i)))

Python: from math import sqrt
from sys import stdin

def isprime(x) :
    if x == 2 : return x
    elif (x < 2) or (x % 2 == 0) : return False
    else :
        i = 3
        while i <= sqrt(x) :
            if x % i == 0 : return False
            i = i + 2
    return x

for Input in stdin :
    result = 0
    for make in range(2, int(Input) + 1) :
        if isprime(make) != False : result += 1
    print(result)

Python: from __future__ import (division, absolute_import, print_function,
                        unicode_literals)
from sys import stdin

def enum_prime(n):
    if n < 2:
        return []
    if n == 2:
        return [2]
    L = list(range(2, n + 1))
    PL = []
    while True:
        PL.append(L[0])
        L = [i for i in L if i % PL[-1] != 0]
        if L[-1] < PL[-1] ** 2:
            return PL + L

for line in stdin:
    print(len(enum_prime(int(line))))

Python: # coding: utf-8

LIMIT = 999999

prime = [0, 1] + [0 if i % 2 == 0 else 1 for i in range(3, LIMIT + 1)]

for i in range(3, LIMIT + 1):
    if prime[i - 1]:
        for j in range(i ** 2, LIMIT + 1, i):
            prime[j - 1] = 0

while True:
    try:
        n = int(input())
    except EOFError:
        break

    print(sum(prime[:n]))

Python: def sieve(n):
	p=[True]*(n+1)
	p[0]=p[1]=False
	for i in range(2,n+1,2):
		if p[i]==True:
			for j in range(i*i,n+1,i):
				p[j]=False
	return p

def solve(n):
		if n<2:return 0
		c=1
		for i in range(3,n+1,2):
			if p[i]==1:
				c+=1
		return c

p=sieve(100000)
while True:
	try:
		n = int(input())
		print(solve(n))
	except EOFError:
		break

Python: # -*- coding: utf-8 -*-

import sys
import os
import math



def Eratosthenes(n):
    lst = [i for i in range(2, n+1)]
    primes = []
    sqrt_n = n ** 0.5

    while True:
        first = lst.pop(0)
        if first < sqrt_n:
            primes.append(first)
            new_lst = []
            for v in lst:
                if v % first != 0:
                    new_lst.append(v)
            lst = new_lst
        else:
            # ??????
            return primes + [first] + lst

s_list = sys.stdin.readlines()
for s in s_list:
    n = int(s)
    lst = Eratosthenes(n)
    print(len(lst))

Python: import math
import sys

def prime_calc(n):
    rootN = math.floor(math.sqrt(n))
    prime = [2]
    data = [i + 1 for i in range(2,n,2)]
    while True:
        p = data[0]
        if rootN < p:
            return len(prime + data)
        prime.append(p)
        data = [e for e in data if e % p != 0]

def main():
    l = []

    for line in sys.stdin:
        l.append(line)        

    for line in l:
        print(prime_calc(line))

if __name__ == "__main__":
    main()

Python: import sys

for input in sys.stdin:
    prime_num = 0
    for i in xrange(int(input)):
        y = i+1
        x = y / 2
        r = 2
        while r <= x:
            if y % r == 0:
                break
            r += 1
        else:
            prime_num += 1
    print(prime_num-1)

Python: import math
def sosu(n) :
    for i in range(3, int(math.sqrt(n))+1, 2) :
        if n % i == 0 :
            return False
    return True

S = [0, 0, 1, 2, 2, 3, 3, 4, 4, 4, 4]
for i in range(11, 1000000) :
    if i % 2 == 0 :
        S.append(S[i-1])
    elif sosu(i) :
        S.append(S[i-1]+1)
    else :
        S.append(S[i-1])


while True :
    try :
        n = int(input())
    except EOFError :
        break
    
    print(S[n])

Python: def prime_judge(n):
    if n==1:
        return False
    elif n==2:
        return True
    elif n%2==0:
        return False
    else:
        sqrt_num=int(n**0.5)+1
        for i in range(3,sqrt_num, 2):
            if n%i==0:
                return False
        return True

prime=[0]
for i in range(1,1000000):
    if prime_judge(i):
        prime.append(prime[-1]+1)
    else:
        prime.append(prime[-1])

while 1:
    try:
        print(prime[int(input())])     
    except:
        break

Python: # PrimeNumber
# エラトステネスの篩

from itertools import product
import math

if __name__ == "__main__":
    while True:
        try:
            # 数値の入力があった
            n = int(input())
            nlist = []
            nlist2 = []
            plist = []

            # for i in range(2, n + 1):
            #    nlist.append(i)  # [2,3,4,5,6,...,n]
            nlist = range(2, n + 1, 1)

            while True:
                #print(nlist, " ", math.sqrt(n))
                sqrtn = math.sqrt(n)
                if nlist[0] > sqrtn:  # 終了条件
                    #plist.append(map(int,nlist))
                    plist.extend(nlist)
                    break
                else:
                    plist.append(nlist[0])

                    #i = 0
                    for j in nlist:
                        if j % nlist[0] != 0:
                            #nlist.pop(i)
                            #nlist.remove(j)
                            nlist2.append(j)
                            #i += 1
                    nlist = nlist2
                    nlist2 = []
            #print("fin: {}".format(plist))
            print(len(plist))

        except EOFError:
            break  # escape from while loop

pass
#