Go: package main

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

var sc = bufio.NewScanner(os.Stdin)

func main() {
	var primeCount int
	for sc.Scan() {
		input := nextInt()
		for i := 0; i <= input; i++ {
			if IsPrime(i) {
				primeCount++
			}
		}
		fmt.Printf("%d\n", primeCount)
		primeCount = 0
	}
}

func IsPrime(num int) bool {
	switch {
	case num == 2 || num == 5:
		return true
	case num < 2 || num%2 == 0 || num%5 == 0:
		return false
	}
	sqrt := math.Sqrt(float64(num))
	for i := 3; i <= int(sqrt); i += 2 {
		if num%i == 0 {
			return false
		}
	}
	return true
}

func next() string {
	return sc.Text()
}

func nextInt() int {
	a, _ := strconv.Atoi(next())
	return a
}

Python: from math import sqrt

I_list=[]

#input syutoku

while True:

	try:

		k=int(input())

		I_list.append(k)

	except:

		break



I_max=max(I_list)

#create list (I_max=100 -> [3,5,7,...,99])

odd_list=[x for x in range(3,I_max+1,2)]

#print(W_list)



P_list=[2]



p=0

#print(I_list)

ct=0

while p<=int(sqrt(I_max)):

	p=odd_list.pop(0)

	P_list.append(p)

	P_baisuu=[p*x for x in range(1, int(I_max/p) +1 )]

	K_list=set(odd_list)-set(P_baisuu)

	odd_list=sorted(list(K_list))

#	print("P_list=")

#	print(P_list)

#	print("odd_list=")

#	print(odd_list)



prime_list=P_list+odd_list

#print("prime_list=")

#print(prime_list)



for i in I_list:

	w=[j for j in prime_list if j<=i ]

	print(len(w))

Python: def so(x):
    a=[]
    b=[True]*(n+1)
    b[0]=False
    b[1]=False
    for i in range(2,int(x**0.5)+1):
        if not b[i]:
            continue
        for j in range(i*2,n+1,i):
            b[j]=False
    for k in range(len(b)):
        if b[k]:
            a.append(k)
    print(len(a))
while True:
    try:
        n = int(input())
    except:
        break
    so(n)

Python: import sys
import math

# Sieve of Eratosthenes
N = 999999
searchList = list(range(3, N + 1, 2))
primes = [2]
while True:
  top = searchList.pop(0)
  primes.append(top)
  if top > math.sqrt(N):
    break
  searchList = [s for s in searchList if s % top != 0]
primes.extend(searchList)

# solve
for line in sys.stdin:
  try:
    n = int(line)
    ans = [i for i in primes if i <= n]
    print(len(ans))
  except:
    break

Python: prime=[True]*1000000
np=[0]*1000000
for i in range(2,1000):
    if prime[i]:
        for j in range(i*2,1000000,i):
            prime[j]=False

while True:
    try:
        n=int(input())
    except:
        break
    print(sum(prime[2:n+1]))

Python: def get_input():
    while True:
        try:
            yield ''.join(input())
        except EOFError:
            break

MAX = 1000000
primes = list()
for i in range(MAX):
    primes.append(True)
primes[0] = False
primes[1] = False

for i in range(2, MAX):
    j = i + i
    while j < MAX:
        primes[j] = False
        j = j + i

N = list(get_input())
for l in range(len(N)):
    n = int(N[l])
    ans = 0
    for i in range(n+1):
        if primes[i]:
            ans = ans + 1
    print(ans)

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 a[i*2::i]]
for e in sys.stdin:print(len([i for i in li[:int(e)+1]if i]))

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: from math import *
search_list = []
search_list_ref = []
prime_list = []
prime_list_ref = []
target1,target2,num = 0,0,2
i,j,k = 0,0,0
flag = 0
def get_input():
    while True:
        try:
            yield ''.join(input())
        except EOFError:
            break
if __name__ == "__main__":
    array = list(get_input())
    print("/*------------------------------------*/")
    for i in range(len(array)):
        print(str(array[i]) + "?????????????´???°????±??????????")
    #??\????????¨?????????????????????????????§?´???°????????°?????¢?´¢??????
        #?????????sqrt(int(array[i]))?????§????????§?´???°??????????????????
        ref_target = int(sqrt(int(array[i])))
        search_list_ref.append(2)
        search_list_ref.append(ref_target)
        while target1 < ref_target:
            if search_list_ref == []:
                break
            prime_list_ref.append(search_list_ref[0])
            target1 = search_list_ref[0]
            search_list_ref.remove(target1)
            if target1 > ref_target:
                break
            num = target1
            if target1 == 2:
                for num in range(2,ref_target):
                    if (num % target1 != 0):
                        search_list_ref.append(num)
                if ref_target != 3:
                        search_list_ref.remove(ref_target)
            else:
                for j in search_list_ref:
                    if j % target1 == 0:
                        search_list_ref.remove(j)

        prime_list_ref = prime_list_ref + search_list_ref
        search_list.append(2)
        search_list.append(int(array[i]))

        #?????????????????¬??\?±????????????°?????????????´???°????±??????????
        while target2 < sqrt(int(array[i])):
            prime_list.append(search_list[0])
            target2 = search_list[0]
            search_list.remove(target2)
            if target2 > sqrt(int(array[i])):
                break
            num = target2
            if target2 == 2:
                for num in range(2,int(array[i])):
                    for k in prime_list_ref:
                        if num % k != 0:
                            flag = 1
                        else:
                            flag = 0
                            break
                    if flag == 1:
                        search_list.append(num)
                search_list.remove(int(array[i]))
                prime_list_ref.pop(0)
                search_list[1:1] = prime_list_ref
                break
            elif target2 not in prime_list_ref:
                for j in search_list:
                    if j % target2 == 0:
                        search_list.remove(j)
                break
            else:
                pass
        prime_list = prime_list + search_list
        #print(array[i] + "??\???????´???°????????°???" + str(len(prime_list)))
        print(str(len(prime_list)))
        del search_list_ref[:]
        del prime_list_ref[:]
        del search_list[:]
        del prime_list[:]
        target1 = 0
        target2 = 0
        print("/*------------------------------------*/")

Python: import math

P = []
# 素数一覧リスト
Max = 1000000

def Era(P, Max) :
    D = list(range(2, Max))
    limit = math.sqrt(Max)
    while True :
        p = D[0]

        if limit <= p :
            P += D
            return P

        P.append(p)
        D = [d for d in D if d % p != 0]
        # D に含まれる値かつ p で割り切れない値をリスト化

Era(P, Max)

while True :
    try :
        n = int(input())

        if n == 1 :
            print(0)
        elif n == 2 :
            print(1)
        elif n >= max(P) :
            print(len(P))
        else :
            for i in range(n + 1) :
                if P[i] == n :
                    print(i + 1)
                    break
                elif P[i] > n :
                    print(i)
                    break

    except :
        break

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 = []
    for make in range(2, int(Input) + 1) :
        if isprime(make) != False : result.append(make)
    print(len(result))