Go: package main

// https://ja.wikipedia.org/wiki/%E3%82%A8%E3%83%A9%E3%83%88%E3%82%B9%E3%83%86%E3%83%8D%E3%82%B9%E3%81%AE%E7%AF%A9

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() (int, error) {
	return strconv.Atoi(nextString())
}

func main() {
	scanner.Split(bufio.ScanWords)

	for {
		n, err := nextInt()
		if err != nil {
			break
		}
		maybePrime := make([]bool, n+1)
		for i := 0; i <= n; i++ {
			maybePrime[i] = true
		}

		maybePrime[0] = false
		maybePrime[1] = false
		for i := 2; i <= int(math.Sqrt(float64(n)))+1; i++ {
			j := i * 2
			for j <= n {
				maybePrime[j] = false
				j += i
			}
		}

		nPrimes := 0
		for _, p := range maybePrime {
			if p {
				nPrimes++
			}
		}
		// fmt.Println(maybePrime)
		fmt.Println(nPrimes)
	}
}

Python: # coding: utf-8

import sys
import math


if __name__ == '__main__':
	input_list = sys.stdin.readlines()

	for num in input_list:
		target_number = int(num.replace('\n', ''))
		serial_number_list = [r for r in range(2, target_number + 1)]
		multiple_list = []

		while math.sqrt(target_number) >= serial_number_list[0]:
			serial_number = serial_number_list[0]
			i = 1
			multiple_list.append(serial_number)

			while target_number >= serial_number * i:
				
				if serial_number * i in serial_number_list:
					serial_number_list.pop(serial_number_list.index(serial_number * i))

				i += 1

		print(multiple_list)

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

Python: import math

def Eratos(n):
	primes = [2]
	if n % 2 == 0:
		num = [2*i+1 for i in range(1,n/2)]
	else:
		num = [2*i+1 for i in range(1,(n+1)/2)]
	tmp = []

	top = 1
	while top < math.sqrt(n):
		top = num[0]
		for i in range(1,len(num)):
			if num[i] % top != 0:
				tmp.append(num[i])
		num = tmp
		tmp = []
		primes.append(top)
	for i in range(len(num)):
		primes.append(num[i])
	return primes

def list_count(list_a,n):
	cont = 0
	for i in range(len(list_a)):
		if list_a[i] > n:
			break
		else:
			cont += 1
	return cont

primes = Eratos(1000000)
while True:
	try:
		n = int(input())
		print(list_count(primes,n))
	except EOFError:
		break

Python: import math
def prime(n):
    plist = [1 for i in range(n)]
    pivot = int(math.sqrt(n))
    plist[0] = 0
    if n <= 1:
        return 0
    if n == 2:
        return 1
    if n == 3:
        return 2
    else:
        for i in range(2,pivot+1):
            if plist[i-1] == 0:
                continue
            else:
                for j in range(2*i,n+1,i):
                    plist[j-1] = 0
    psum = sum(plist)
    return psum

import sys
while True:
    line = sys.stdin.readline()
    if not line: break
    n = int(line.rstrip('\r\n'))
    print(prime(n))

Python: def checkPrime(number):
    if number == 2:
        return True
    if number % 2 == 0:
        return False

    i = 3
    while (i ** 2 < number + 1):
        if number % i == 0:
            return False
        i += 2

    return True

p = [True for i in range(0, 1000000)]

p[0] = 0
p[1] = 0
for i in range(2, len(p)):
    p[i] = p[i - 1]
    if checkPrime(i):
        p[i] += 1

while True:
    try:
        print(p[int(input())])
    except:
        break

Python: while True:
    ss=input()
    if len(ss)==0:
        break
    s=int(ss)+1
    if s<2:
        print(0)
    else:
        list=[True]*s
        list[0]=False
        list[1]=False
        i=2
        while i**2<=s-1:
            j=i*2
            while j<=s-1:
                list[j]=False
                j+=i
            i+=1
        print(list.count(True))

Python: import math
while True:
    try:
        n=int(input())
        num=list(range(n+1))
        num[1]=0
        for i in range(n):
            if num[i]>pow(n,0.5):
                break
            if num[i]==0:
                continue
            for j in range(num[i]*2, n+1, num[i]):
                num[j]=0
        print(n+1-num.count(0))
    except:
        break

Python: import numpy as np
while 1:
	num = int(input())
	n = [] #素数をかくのするためのリスト
	li = [] #2から入力された値までのすべての数を格納するリスト
	
	#2から入力された値までのすべての数を格納
	li = [i for i in range(2,num+1)]
	
	#liリストの0番目が入力された値の平方根以下になるまでloop
	while li[0] <= int(np.sqrt(num)):
		n.append(li[0]) #nリストにliリストの0番目を追加
		sss = li[0] #sssにliリストの0番目を格納
		li = [i for i in li if i % sss != 0] #素数判定
	n.extend(li) #liリストに残った数を素数としてnリストに格納
	print(len(n))

Python: # coding: utf-8

import sys
import math


if __name__ == '__main__':
	input_list = sys.stdin.readlines()

	for num in input_list:
		target_number = int(num.replace('\n', ''))
		serial_number_list = [r for r in range(2, target_number + 1)]
		multiple_list = []

		while math.sqrt(target_number) >= serial_number_list[0]:
			serial_number = serial_number_list[0]
			i = 1
			multiple_list.append(serial_number)

			while target_number >= serial_number * i:
				
				if serial_number * i in serial_number_list:
					serial_number_list.pop(serial_number_list.index(serial_number * i))

				i += 1

		print(multiple_list + serial_number_list)

Python: from sys import stdin

def prime(n: int) -> int:
    Prime = [i for i in range(n+1)]
    for i in range(2,n+1):
            for j in range(2,int(n/i)+1):
                Prime[i*j] = 0
    Prime[0],Prime[1] = 0,0
    print(Prime)
    ans = [i for i in Prime if not(i == 0)]
    return len(ans)


n = int(input())
print(prime(n))

Python: import sys

x = 500000
f = [0, 1] * xx
i = 3

while i * i <= 2 * xx:
    if f[i] == 1:
        j = i * i
        while j <= 2 * xx:
            f[j] = 0
            j += i + i
    i += 2

f.pop(0)
f.pop(1)

for n in sys.stdin:
    i = int(n)
    if i < 2:
        print(0)
    else:
        print(sum(f[:i - 1]))

Python: import sys
m=166666;s=[1]*m;t=[1]*m
for i in range(m):
 if s[i]:
  k=6*i+5
  s[i+k::k]=[0]*len(s[i+k::k])
  t[-2-i+k::k]=[0]*len(t[-2-i+k::k])
 if t[i]:
  k=6*i+7
  s[-2-i+k::k]=[0]*len(s[-2-i+k::k])
  t[i+k::k]=[0]*len(t[i+k::k])
for e in map(int,sys.stdin):
 print([e-1,sum(s[:(e+1)//6])+sum(t[:(e-1)//6])+2][e>3])

Python: # coding: utf-8
# Your code here!

MAX = 1000000
s = [1] * MAX
s[0] = 0
s[1] = 0

start = 2
while True:
    pmb = 0
    for i in range(start, MAX):
        if s[i] == 1:
            pmb = i
            break
   
    if pmb == 0:
        break

    for i in range(pmb ** 2, MAX, pmb):
        s[i] = 0

    start += 1
    
while True:
    try:
        n = int(input())
        
        c = 0
        for i in range(2, n + 1):
            if s[i] == 1:
                c += 1
        print(c)

    except EOFError:
        break

Python: while True:
    try:
        n = int(input())
        count = 0
        if n == 1:
            print("0")
        else:
            a = [2*i for i in range(2, 1000000)]
            b = [3*i for i in range(2, 1000000)]
            c = [5*i for i in range(2, 1000000)]
            d = [7*i for i in range(2, 1000000)]
            for i in range(2, n+1):
                if i not in a and i not in b and i not in c and i not in d:
                    count += 1
            print(count)
    except:
        break

Python: n = 1000000
a = [True for i in range(n)]
i = 3
while i * i < n:
    for j in range(3 * i, n, 2 * i): a[j] = False
    i += 2
 
while True:
    try:
        b = int(input())
    except:
        break
 
    count = int(b >= 2) + sum(a[i] for i in range(3, b + 1, 2))
    print(count)