Go: package main
import (
	"fmt"
	"os"
	"strconv"
	"bufio"
	//"math"
)

var sc = bufio.NewScanner(os.Stdin)

func main(){
	for sc.Scan(){
		n := nextInt()
		fmt.Println(calc(n))
	}
}

func calc(n int)int{
	// エラトステネスで数え上げる
	// 最初から999999まで用意しておいて入力のたびO(1)で出すのとどっちが速いのかはわからん
	eratos := make([]bool, n+1)
	c := 0
	for i:=2; i<len(eratos); i++{
		if eratos[i] == false{
			c++
			for j:=i*i; j<len(eratos); j+=i{
				eratos[j]=true
			}
		}
	}
	return c
}

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

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

Python: import sys
import math
from array import array

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 = array('I',[1]) * N1
m = array('I',[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)

Python: import sys
for ss in sys.stdin:
    s=int(ss)+1
    if s<2:
        print(0)
    else:
        list=[True]*s
        list[0]=False
        list[1]=False
        i=2
        while i**2<=s-1:
            j=i*2
            while j<=s-1:
                list[j]=False
                j+=i
            i+=1
        print(list.count(True))

Python: 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:
            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: def check_prime(goal):
    true_or_false=False
    for i in range(2,goal):
        if goal%i==0:
             true_or_false=True
             break
    if true_or_false==False:
        return True
    else:
        return False

anss=[]
while True:
    try:
        num=int(input())
        num_of_prime=0
        for i in range(2,num+1):
           if check_prime(i):
               num_of_prime+=1
        anss.append(num_of_prime)
    except:
        break

for ans in anss:
    print(ans)

Python: #coding:utf-8
import time
import math
import numpy as np

def flatten(L):
    if isinstance(L, list):
        if L == []:
            return []
        else:
            return flatten(L[0]) + flatten(L[1:])
    else:
        return [L]

def Eratos(data):

    p_list = []
    tmp = []
    num = int(math.sqrt(len(data)))+1
    for i in data:
        i=data[0]
        if i>num:
            break
        else:
            p_list.append(i)
            for j in data:
                if j%i == 0:
                    data.remove(j)
        
    p_list.append(data)
    return p_list

x = int(input())

r_list = list(range(2,(x+1)))
ans = []
ans = Eratos(r_list)

print(len(flatten(ans)))

Python: while True:
    try:
        n=int(input())
    except:
        break
    print(sum(i==2 or pow(2,i-1,i)==1 for i in range(2,n+1)))

Python: A=[
960131, 960137, 960139, 960151, 960173, 960191, 960199, 960217, 960229, 960251, 960259, 960293, 960299, 960329, 960331, 960341, 960353, 960373, 960383, 960389, 960419, 960467, 960493, 960497, 960499, 960521, 960523, 960527, 960569, 960581, 960587, 960593, 960601, 960637, 960643, 960647, 960649, 960667, 960677, 960691, 960703, 960709, 960737, 960763, 960793, 960803, 960809, 960829, 960833, 960863, 960889, 960931, 960937, 960941, 960961, 960977, 960983, 960989, 960991, 961003, 961021, 961033, 961063, 961067, 961069, 961073, 999149, 999169, 999181, 999199, 999217, 999221, 999233, 999239, 999269, 999287, 999307, 999329, 999331, 999359, 999371, 999377, 999389, 999431, 999433, 999437, 999451, 999491, 999499, 999521, 999529, 999541, 999553, 999563, 999599, 999611, 999613, 999623, 999631, 999653, 999667, 999671, 999683, 999721, 999727, 999749, 999763, 999769, 999773, 999809, 999853, 999863, 999883, 999907, 999917, 999931, 999953, 999959, 999961, 999979, 999983]
while True:
    try:
        n=int(input())
        print(A)
    except:
        break

Python: def erato(n):
    s = list(range(n+1))
    s[1] = 0
    for e in s:
        if e:
            for i in range(e*2, n+1, e):
                s[i] = 0
    return s
while True:
    try:
        n = int(input())
        print(len(list(filter(lambda x:x, erato(n)))))
    except:
        break

Python: # -*- coding: utf-8 -*-
from math import sqrt
from bisect import bisect

def inpl(): return tuple(map(int, input().split()))

def primes(N):
    P = [2]
    searched = [False]*(N+1)
    for i in range(3, N+1, 2):
        if searched[i]:
            continue
        P.append(i)
        for j in range(i, N+1, i):
            searched[j] = True
    return P

P = primes(10**6)

try:
    while True:
        print(bisect(P, int(input())))
except:
  pass

Python: def sieve_prime(n): # return prime numbers within [1, n]
  primes = []
  is_prime = [True] * (n+1) # [0, n]
  for i in range(2, n+1):
    if not is_prime[i]:
      continue # need only primes

    primes.append(i)
    for j in range(i*2, n+1, i): # range(i*2, n+1, i) = {i*2, i*3, ...}
      is_prime[j] = False

    """
    Compare the above code with the below one in the view of time complexity
    for j in range(i*2, n+1):
      if j % i == 0:
        is_prime[j] = False
    """
        
  return primes
      
while True:
  try:
    n = int(input())
    print(len(sieve_prime(n))) # because T <= 30, you can simply use sieve_prime every time
  except EOFError:
    break

Python: while t == 0:	
	total = 0
	try:
		n = int(input())
	except:
		break
	else:
	        print(total)

Python: import math

a = [1]*1000000
for i in range(2,1000000):
    for j in range(i+i,1000000)[::i]:
        a[j] = 0

b = [0]*1000000
b[0] = b[1] = 0
for i in range(2,1000000):
    if a[i] == 1:
        b[i] = b[i-1] + 1
    else:
        b[i] = b[i-1]

while True:
    try:
        print(b[int(input())])
    except EOFError:
        break

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())
	except EOFError:
		break
	cnt = 0
	for x in P:
		if x>n:
			break
		cnt += 1
	print(cnt)

Python: from sys import stdin

for limit in stdin:
    limit = int(limit)
    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)

Python: import sys


def primes(n):
    f = []
    for i in range(n + 1):
        if i > 2 and i % 2 == 0:
            f.append(0)
        else:
            f.append(1)
    i = 3
    while i * i <= n:
        if f[i] == 1:
            j = i * i
            while j <= n:
                f[j] = 0
                j += i + i
        i += 2
    return f[2:]


if __name__ == "__main__":
    ps = primes(100)
    for n in sys.stdin:
        i = int(n)
        if i < 2:
            print(i, 0)
        else:
            print(i, sum(ps[:i - 1]))