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: from math import sqrt
from sys import stdin
def isprime(n):
    if n == 1:
        return False
    if n == 2:
        return True
    if n % 2 == 0:
        return False
    for i in range(3, int(sqrt(n))+1):
        if n % i == 0:
            return False
    return True

for n in stdin:
    n = int(n)
    ct = 0
    for i in range(1,n + 1):
        if isprime(i):
            #print (i)
            ct += 1
    print (ct)

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

lst = [i for i in range(2, max(num)+1)]
for i in lst[::-1]:
    for j in range(2, i):
        if i % j == 0:
            lst.pop(lst.index(i))
            break

for i in num:
    for j in lst:
        if i < j:
            print(lst.index(j))
            break
        elif i == j:
            print(lst.index(j)+1)
            break

Python: def ct(num):
    primel=[2]
    for i in range(num):
        n=i+1
        if i==0 or i==1:continue 
        for e in primel:
            if n%e==0:break
        else:primel.append(n)
    return len(primel)        
    
while True:
    try:raw=[int(i) for i in input().split(" ")]
    except:break
    a=raw[0]
    print(str(ct(a)))

Python: import sys
m=10**5//2
a=[0,0,1]+[1,0]*m
for i in range(3,999):
 if a[i]:a[i*2::i]=[0]*len(a[i*2::i])
for e in sys.stdin:print(sum(a[:int(e)+1]))

Python: from itertools import takewhile
primes = [2, 3, 5, 7]
append_prime = primes.append
upper = 10


def is_prime(num):
    for p in primes:
        if num % p == 0:
            return False
    return True


def calc_prime(num):
    for i in range(upper + 1, num + 1):
        if is_prime(i):
            append_prime(i)

for s in sys.stdin:
    print(primes)
    n = int(s)
    if upper < n:
        calc_prime(n)
        upper = n
        print(len(primes))
    else:
        print(len(tuple(takewhile(lambda x: x <= n, primes))))

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

Python: import sys
m=10**6;a=[0,0]+[1]*m
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(sum(a[:int(e)+1]))

Python: import bisect

primes = [0, 0] + [1] * 999999
for i in range(2, 1000):
    if primes[i]:
        for j in range(i*i, 1000000, i):
            primes[j] = 0

primes = [i for i, v in enumerate(primes) if v]
while True:
    try:
        n = int(input())
    except:
        break
    print(bisect.bisect(primes, n))

Python: import sys

l = [True] * 100000
for i in range(2, 100000):
    if (l[i - 1]):
        for j in range(i ** 2 - 1, 100000, i):
            l[j] = False
n = [int(line) for line in sys.stdin]
for j in n:
    print(l[1:int(j)].count(True))

Python: import math

isPrime = [True] * 1000000
primes = []
def eratos(n):
    isPrime[0] = isPrime[1] = False
    for i in range(2,int(math.sqrt(n))):
        if isPrime[i]:
            j = 2 * i
            while j <= n:
                isPrime[j] = False
                j = j + i
eratos(999999)

while True:
    try:
        num = int(input())
        ans = 0
        for i in range(0,num + 1):
            if isPrime[i]:
                ans += 1
        print(ans)
    except:
        break

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

Python: import sys

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

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()