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: def get_input():
    while True:
        try:
            yield ''.join(input())
        except EOFError:
            break
if __name__ == '__main__':
    array = list(get_input())
    cnt,flag = 0,0
    for i in range(len(array)):#?????°????????°????????????
        for j in range(2,int(array[i])+1):#1??????????´??????¢??????????´???°??¢?´¢????????????
            flag = 0
            if j == 2:
                flag = 1
            for k in range(2,j):
                if j % k == 0:
                    flag = 0
                    break
                flag = 1
            if flag == 1:
                cnt += 1  
        print(cnt)
        cnt = 0

Python: primes = [0, 0] + [1]*999999
for i in range(2, 1001):
    if primes[i]:
        for j in range(i*i, 1000001, i):
            primes[j] = 0

while True:
    try:
        n = int(input()) + 1
        print(sum([1 for i in range(n) if primes[i]]))
    except:
        break

Python: # coding: utf-8


import math

def sieve_of_erastosthenes(num):
    input_list = [False if i % 2 == 0 or i % 3 == 0 or i % 5 == 0 else True for i in range(num)]
    input_list[0] = input_list[1] = False
    input_list[2] = input_list[3] = input_list[5] = True
    sqrt = math.sqrt(num)

    for serial in range(3, num, 2):
        
        if serial >= sqrt:
            # print([i for i, b in enumerate(input_list) if b == True])
            return sum(input_list)

        for s in range(serial ** 2, num, serial): 
            input_list[s] = False


if __name__ == '__main__':
    while True:
        try:
            print(sieve_of_erastosthenes(int(input())))
        except:
            break

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

Python: import sys

MAX = 999999
L = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997]

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

def is_prime_2(n):
  a = int(n ** 0.5)
  for i in L:
    if i > a:return True
    if n % i == 0:return False
  return True

def prime_count(n):
  result = 0
  if n >= 2:result+=1
  for i in range(3,n+1,2):
    if is_prime_2(i):result+=1
  return result

def prime_list(n):
  result = []
  if n >= 2:result.append(2)
  for i in range(3,n+1,2):
    if is_prime(i):result.append(i)
  return result

L2 = prime_list(MAX)

def prime_count_2(n):
  for i,v in enumerate(n):
    if n > v:return i
  return len(L2)

for n in sys.stdin:
  print(prime_count(int(n)))

Python: import sys,random

rand = random.randint

def prime(n):
	if n == 2: return True
	if n < 2 or n & 1 == 0: return False
	return pow(2, n-1, n) == 1

a = [prime(i) for i in range(1000000)]

for s in sys.stdin:
	i = int(s)
	print(a[:i+1].count(True))

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

def main():
    List=[]
    while True:
        try:
            IN=int(input())
            for i in range(2,IN+1):
                List.append(i)

            j=0
            while (j+1)<len(List):
                l=len(List)
                for k in range(l-1,j,-1):
                    a=List[k]%List[j]
                    if a==0:
                        del List[k]
                    else:
                        pass

                j+=1

            print(len(List))
                    
        
        except:
            break

Python: import sys
x = 1000000
xx = 500000
f = [1, 0] * xx
f[0] = 0
f[1] = 1
i = 3
while i < x:
    if f[i] == 1:
        j = i
        y = x // i + 1
        while j < y:
            f[j] = 0
            j += i + i
    i += 2

for n in sys.stdin:
    i = int(n)
    print(sum(f[:i]))

Python: def isprime(num):
   i = 2
   count = 0
   while i< num:
       if num % i == 0:
           count += 1
       i += 1
   if count == 0:
       return 1
   else:
       return 0
num = int(input())
count_prime = 0
for i in range(2,num):
   if(isprime(i) == 1):
       count_prime += 1
print(count_prime)

Python: def IsPrime(arr):
  arr[0] = 0
  arr[1] = 0
  i = 2
  while i**2 <= len(arr):
    if arr[i]:
      for j in range(i*2,len(arr),i):
        arr[j] = 0
    i += 1
  return arr

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

n_max = max(num)
prime_array = IsPrime([1 for i in range(n_max+1)])
for i in range(len(num)):
  counter = 0
  for j in range(num[i]+1):
    counter += prime_array[j]
  print(counter)

Python: import sys

def check(q):
    if q == 2: return True
    if q&1 == 0: return False
    return pow(2, q-1, q) == 1

l = [d for d in range(2, 1000000) if check(d)]

for line in sys.stdin:
    N = int(line.rstrip())
    print(len([i for i in l if N>i]))

Python: import sys
  
lalala = 1000000//30 + 1
f = ([1,0,0,0,1,0,1,0,0,0,1,0,1,0,0,0]+[1,0]*7 ) * lalala
f = [0,0,1,1] + f[3:-20]

i = 5
while i < 1000:
    if f[i] == 1:
        j = i * i
        while j <= 1000000:
            f[j] = 0
            j += i + i
    i += 2

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

Python: import sys
import math
M = 1000000
B = int(math.sqrt(M)+1)//6+1
N = M//6
N1 = N+1 if M % 6 == 5 else N
N2 = N+1 if M % 6 >= 1 else N
l = [1] * N1
m = [1] * N2
i = 5
ini = 4
for p in range(B):
    if l[p] == 1:
        l[p+i::i] = [0] * len(l[p+i::i])
        m[ini-1::i] = [0] * len(m[ini-1::i])
    if m[p] == 1:
        m[p+i+2::i+2] = [0] * len(m[p+i+2::i+2])
        l[ini+1::i+2] = [0] * len(l[ini+1::i+2])
    i += 6
    ini += 5
 
for i in sys.stdin:
    n = int(i)
    r =  n-1 if n < 3 else sum(l[0:(n+1)//6])+sum(m[0:(n-1)//6])+2
    print(r)