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] = 1
        }
        primes[0] = 0
        primes[1] = 0
        Soe()
}

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

Python: # coding: utf-8
# Here your code !
import math
 
def is_prime_num(in_num):
    cnt = 0
    if in_num == 2:
        return True
    elif in_num <= 1:
        return False
    elif in_num % 2 == 0:
        return False
    else:
        if pow(2, in_num-1, in_num) == 1:
            max_num = int(math.sqrt(in_num)+1)
            for j in range(3, max_num, 2):
                if in_num % j == 0:
                    cnt = cnt + 1
                    break
                         
            if cnt == 0:
                #??´????°
                return True
            else:
               return False
        else:
            return False

while True:
    try:
        n = int(input())
        prime_cnt = 0
        if n >= 2:
            #?????????2???????????????
            prime_cnt = prime_cnt + 1

        for i in range(3, n+1, 2):
            if is_prime_num(i):
                prime_cnt = prime_cnt + 1
                 
 
        print(str(prime_cnt))
    except:
        break

Python: def isPrime(x):
    if x==2:
        return True
    if x<2 or x%2==0:
        return False
    if pow(2,x-1,x)==1:
        return True
    else:
        return False
while 1:
    try:
        n=input()
        ct=0
        for i in xrange(n+1):
            if isPrime(i):
                ct+=1
        print(ct)
    except:
        break

Python: def get_prime_set(ub):
    from itertools import chain
    from math import sqrt

    if ub < 4:
        return ({}, {}, {2}, {2, 3})[ub]

    ub, ub_sqrt = ub+1, int(sqrt(ub))+1
    primes = {2, 3} | set(chain(range(5, ub, 6), range(7, ub, 6)))
    du = primes.difference_update
    for n in chain(range(5, ub_sqrt, 6), range(7, ub_sqrt, 6)):
        if n in primes:
            du(range(n*3, ub, n*2))

    return primes


import sys
from bisect import bisect_right
primes = list(get_prime_set(999999))
print(*(bisect_right(primes, int(n)) for n in sys.stdin), sep="\n")

Python: from math import sqrt,floor
from sys import stdin

def cntPrime(n):
    mx = sqrt(n)
    if n % 2 == 0:
      l = [0, 1] + [1, 0] * (int(n/2) - 1)
    else:
      l = [0, 1] + [1, 0] * (int(n/2) - 1) + [1]
    c = 3
    while c < mx:
        for k in range(c*2, n+1, c):
            l[k-1] = 0
        c = l[(c+1):].index(1) + c +2
        while c % 2 == 0:
            c = l[(c+1):].index(1) + c +2
    return l
t = cntPrime(1000000)
for n in stdin:
    n = int(n)
    print(sum(t[:n]))

Python: import math
def kosu(n):
    l=[]
    sosu = [True] * (n + 1)
    sosu[0]= False
    sosu[1]= False
    for i in range(2,math.floor(math.sqrt(n))+1):
        if not sosu[i]:
            continue
        for j in range(i*2,n+1,i):
            sosu[j] = False
    for i in range(len(sosu)):
        if sosu[i]:
            l.append(i)
    return(l)
    
while True:
    try:
        n = int(input())
    except EOFError:
        break
    print(len(kosu(n)))

Python: limit = int(input(""))
arr = [2,3,5,7]
def PrimeNumber(arr,number):
    for i in arr:
        if (number%i==0):
            return False
    return True

for i in range(2,limit+1):
    if(PrimeNumber(arr,i)):
        arr.append(i)

        
count = 0
for i in arr:
    if (i>limit):
        break
    else:
        count += 1
    
print(count)
print()

Python: while True:
    try:
        r = int(input())

        alist = []

        for x in range(2, r+1):
            if x != 2 and x != 3 and x != 5:
                if x % 2 != 0 and x % 3 != 0 and x % 5 != 0:
                    alist.append(x)
            else:
                alist.append(x)

        print(len(alist))
    except EOFError:
        break

Python: import sys
for line in sys.stdin:
    n = int(line)
    arr = [i for i in range(0,n+1)]
    k = 2
    while k**2 <= n:
        for i in range(len(arr)):
            if arr[i]%k == 0 and arr[i] != 2:
                arr[i] = 0
        print(k, arr)
        k += 1
    count = 0
    for i in range(len(arr)):
        if arr[i] != 0 and arr[i] != 1:
            count += 1
    print(count)

Python: import sys

for input in sys.stdin:
    prime_num = 0
    for i in range(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 sys
array = []
for i in sys.stdin:
  array.append(int(i))
m=max(array)
prime = [1]*(m+1)
prime[0] = prime[1] = 0
for i in range(2,int(m**0.5)+1):
  if prime[i] == 1:
    for j in range(i*i, m+1, i):
      prime [j] = 0
for i in range(len(array)):
  print(sum(prime[:array[i] + 1]))

Python: limit = int(input(""))
arr = [2,3,5,7]
def PrimeNumber(arr,number):
    for i in arr:
        if (number%i==0):
            return False
    return True

for i in range(2,limit+1):
    if(PrimeNumber(arr,i)):
        arr.append(i)

        
count = 0
for i in arr:
    if (i>limit):
        break
    else:
        count += 1
    
print(count)
print()

Python: import sys
a=[1]*500000
for i in range(3,999,2):
 if a[i//2]:a[i*i//2::i]=[0]*((499999-i*i//2)//i+1)
for e in map(int,sys.stdin):print([e-1,sum(a[:(e+1)//2])][e>3])

Python: import sys
import math

MAXNUM=1000000
SQRT=math.sqrt(MAXNUM)

def eratosthenes():
    l = [1]*MAXNUM
    l[0:2]=[0]*2
    l[4:MAXNUM:2] = [0]*len(l[4:MAXNUM:2])

    for i in range(3,1000,2):
        l[i*i:MAXNUM:i*2] = [0]*len(l[i*i:MAXNUM:i*2])

    return l

primes = eratosthenes()
for i in sys.stdin:
    n = int(i)
    print(sum(primes[0:n+1]))

Python: import math
b=[]
b.append(1)
b.append(2)
count=1
s=0
while s<30:
    try:
        x=int(input())
        if x>b[count]:
            for i in range(b[count]+1,x+1):
                count1=0
                
                for j in range(2,int(math.sqrt(i))+1):
                    if i%j==0:
                        count1=1
                        break
                if count1==0:
                    count+=1
                    b.append(i)
            print(count)
            print(b)
        else:
            for i in range(count+1):
                if b[i]>x:
                    print(i-1)
                    break
                elif b[i]==x:
                    print(i)
                    break
        s+=1
    except EOFError:
        break

Python: import sys
a=[0,0]+[1]*10**6
for i in range(999):
 if a[i]:a[i*2::i]=[0 for j in[0]*len(a[i*2::i])]
for e in sys.stdin:print(sum(a[:int(e)+1]))

Python: MAX=1000000
B=[]
def P(MAX,B):

    A=[i for i in range(2,MAX+1)]
    lim=MAX**(1/2)
    while True:
        p=A[0]
        if p>lim:
            B+=A
            return B
        else:
            B.append(p)
            A=[i for i in A if i%p!=0]
            
P(MAX,B)
while True:
    try:
        n=int(input())
        if n==1:
            print(0)
        elif n>=max(B):
            print(len(B))
        else:
            for i in range(n+1):
                if B[i]==n:
                    print(i+1)
                    break
                if B[i]>n:
                    print(i)
                    break

    except:
        break