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: def primes(n):
    is_prime = [True] * (n + 1)
    is_prime[0] = False
    is_prime[1] = False
    
    for i in range(2, int(n**0.5) + 1):
        if is_prime[i] == False:
            continue
            
        for j in range(i * 2, n + 1, i):
            is_prime[j] = False
            
    return [i for i in range(n+1) if is_prime[i]]

while True:
    try:
        n = int(input())
        print(len(primes(n)))
    except:
        break

Python: from math import sqrt
from sys import stdin

def pm(n):
    l = list(range(3,n+1)[0::2])
    p = 3
    i = 0
    p = l[i]
    m = sqrt(n)+1
    while p <= m:
        l = l[:i+1] + [n for n in l[i+1:] if n%p != 0]
        i += 1
        p = l[i]
    return len(l) + 1

for n in stdin:
    print (pm(int(n)))

Python: import sys


def count_prime(n):
    global count, pool
    if not pool:
        return count
    p = pool[0]
    while p <= n:
        pool = tuple(i for i in pool if i % pool[0])
        count += 1
        if not pool:
            break
        p = pool[0]
    return count


inset = list(map(int, sys.stdin))
max_in = max(inset)
pool, count = tuple(range(3, max_in + 1, 2)), 1 if max_in > 1 else 0
inset = [(n, i) for i, n in enumerate(inset)]
inset.sort()
outset = [(t[1], count_prime(t[0])) for t in inset]
outset.sort()

print('\n'.join(map(str, [t[1] for t in outset])))

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(sum(a[:int(e)+1]))

Python: import sys
m=10**6;a=[1]*m;a[0:2]=0,0
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


def is_prime(n, primes):
    for prime in primes:
        if prime ** 2 > n:
            return True
        if n % prime  == 0:
            return False
    return True


def count_prime():
    primes = [2, 3]
    for i in range(5, 999999, 2):
        if is_prime(i, primes):
            primes.append(i)

    return primes

primes = count_prime()

for line in sys.stdin:
    n = int(line)
    count = 0

    for i in range(2, n+1):
        if i in primes:
            count += 1

    print(count)

Python: from math import sqrt
from sys import stdin
def pm(n):
    l = list(range(3,n+1)[0::2])
    p = 3
    i = 0
    p = l[i]
    m = sqrt(n)+1
    while p <= m:
        l = l[:i+1] + [n for n in l[i+1:] if n%p != 0]
        i += 1
        p = l[i]
    return len(l) + 1


for i in stdin:
    print(pm(int(i)))

Python: import sys
def fact(n):
    ret = [1]
    for i in range(2,int(n//2)+1):
        if n%i==0:
            ret.append(i)
    return ret
def isPrime(n):
    if n<=1:
        return False
    if n==2:
        return True
    if fact(n)==[1]:
        return True
    else:
        return False
lines = sys.stdin.readlines()
for line in lines:
    inp = int(line)
    s=0
    for i in range(2,inp+1):
        if isPrime(i):
            s+=1
    print (s)

Python: import sys
a=[0,0]+[1]*10**6
for i in range(999):
 if a[i]:
  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
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
for line in sys.stdin:
   num = int(line)
   count_prime = 0
   for i in range(2,num+1):
       if(isprime(i) == 1):
           count_prime += 1
   print(count_prime)
else:
   exit()

Python: import math

def Eratos(n):
	primes = [2]
	num = [2*i+1 for i in range(1,n//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 sys

for line in sys.stdin:
  try:
    n = int(line)
    primes = [2]
    for i in range(3, n + 1):
      primes.append(i)
      for p in primes:
        if i % p == 0 and i != p:
          primes.pop()
          break
    ans = [i for i in primes if i <= n]
    print(len(ans))
  except:
    break

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 sqrt
cash = {}
def isprime(n):
    if n in cash:
        return cash[n]
    for i in range(3, int(sqrt(n)+1))[0::2]:
        if n % i == 0:
            cash[n] = 0
            return 0
    cash[n] = 1
    return 1

from sys import stdin
cash2 = {}
for i in stdin:
    i = int(i)
    c = sum(isprime(n) for n in range(2, i+1)[1::2]) + 1
    print(c)

Python: 
def pi_x(n):
    '''
    pi_x(n)[i] = pi(i)となるようにする
    エラトステネスの篩→O(n log log n)
    '''
    prime = []
    is_prime = [True] * (n + 1) #is_prime[i] = Trueならiは素数
    is_prime[0] = False
    is_prime[1] = False
    for i in range(2, n+1):
        if is_prime[i]:
            prime.append(i)
            for j in range(2 * i, n + 1, i):
                is_prime[j] = False
    prime_accum = [0] * (n + 1)
    for i in range(1, n + 1):
        prime_accum[i] = prime_accum[i - 1] + is_prime[i]
    return prime_accum

import sys

P = pi_x(10 ** 6)
a  = []
for line in sys.stdin:
    a.append(int(line))
for num in a:
    print(P[num])

Python: import sys

p = [0] * 1000000
v = [0] * 1000000
for i in range(2, 1000000):
    for n in range(i + i, 100000, i):
        p[n] = True
    v[i] = v[i - 1] + 1 if p[i] == False else v[i - 1]

for m in sys.stdin:
    print(v[int(m.replace("\n", ""))])

Python: import sys
import math as mas

def sieve(n):
	p=[True for i in range(n+1)]
	p[0]=p[1]=False
	end=int(n**0.5)
	for i in range(2,end+1):
		if p[i]:
			for j in range(i*i,n+1,i):
				p[j]=False
	return p
	
sosu=sieve(1000010)
for i in sys.stdin:
	t=int(i)
	if t<2:print(0)
	elif t==2:print(1)
	else:print(1+sum(sosu[t] for t in range(3,int(i)+1,2)))

#	a,b=map(int,i.split())
#	print(gcd(a,b),lcm(a,b))

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])
[print([e-1,sum(a[:(e+1)//2])][e>3])for e in map(int,sys.stdin)]

Python: def Eratosthenes(n):
	N = {i:True for i in range(2,n+1)}
	primeNumbers = []
	for i in range(2,n+1):
		if N[i]:
			primeNumbers.append(i)
			j = i*2
			while j<=n:
				N.update({j:False})
				j += i
	return primeNumbers

while True:
	P = Eratosthenes(999999)
	try:
		n = int(input())
		print(len([x for x in P if x<=n]))
	except EOFError:
		break