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
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <string>
#include <set>
#include <functional>

static int const MAX(1000000);

class Mod{
	const int n;
	public:
		Mod(const int _n):n(_n){}
		bool operator()(const int _src){
			return ! (_src % n);
		}
};

const std::vector<int> Eratosthenes(std::set<int>& src){
	std::vector<int> result;
	int cnt(0);
	while(!src.empty()){
	  int n(*src.begin());
		result.push_back(n);
		Mod mod(n);
		//std::set<int>::iterator it= std::remove_if( src.begin(), src.end(), mod );
		// n>(MAX/2) ? std::remove( src.begin(), src.end(), n ) :
		for(int i(n);i<MAX;i+=n)  {
		std::set<int>::iterator it= src.find(i);
		if(it!=src.end())
		   src.erase(it );
		}    
		//src.erase(it,src.end());
	}
	return result;
}


int main(int,char**){
	std::set<int> vec;
	int max_2(MAX-MAX/2-MAX/3-MAX/5+MAX/6+MAX/10+MAX/15-MAX/30+3);
	//	vec.reserve(max_2);
	for(int i(3);i<=MAX;i+=2){
		if(i!=3 && i%3==0) continue;
		if(i!=5 && i%5==0) continue;
		vec.insert(i);
	}
	std::vector<int> primes;
	primes.reserve(10000);
	primes =Eratosthenes(vec);
	int n;
	while(std::cin >>n){
		std::vector<int>::const_iterator const it= std::upper_bound(primes.begin(),primes.end(),n);
		int off=it -primes.begin();
		if(n>=2){ ++off; }
		std::cout << off <<std::endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <cmath>
#define MAX_N 1000000

int main(){
    bool p[MAX_N+1];    // p[NUM] : NUM is Prime?
    int n;

    for(int i = 0; i <= MAX_N; i++) p[i] = true;

    for(int i = 1; i <= MAX_N; i++){
        if(i == 1) p[i] = false;
        else{
            if(p[i]){
                for(int j = 2; i * j <= MAX_N; j++){
                   p[i*j] = false;
                }
            }
        }
    }
 
    // for(int i = 0; i <= MAX_N; i++) if(p[i]) printf("%d\n",i);
    
    while(scanf("%d", &n)){
        int count = 0;
        for(int i = 1; i <= n; i++){
            if(p[i])count++;
        }
        printf("%d\n", count);
    }
    return 0;
}

C++: #include <stdio.h>
#include <stdlib.h>
#include <string.h>

int prime(int n) {
  int k;
  for(k = 2; k * k <= n; k++) {
    if(n % k == 0) return 0;
  }
  return 1;
}

int cntPrime(int n) {
  int cnt = 0, i, k;
  for(i = 2; i <= n; i++) {
    cnt += prime(i);
  }
  return cnt;
}

int main() {
  int a;
  int arg[1024] = { 0 };
  int cnt = 0;
  while(scanf("%d", &a) != EOF) {
    printf("%d\n", cntPrime(a));
  }
  int i;
  for(i = 0; i < cnt; i++) {
  }
}
~                                                                                                       
~                                                                                                       
~

C++: #include <stdio.h>
const int MAX_V = 999999;//999999?????§????´???°??¨?????????
int main(){
	int prime [MAX_V];//??¨?????????????????????????????????
	int sum[MAX_V+1];//?´????????????????
	int i, k, n;
	for(i = 2; i <= MAX_V; i++){
		prime[i] = 1;
	}
	for(i = 2; i*i <= MAX_V; i++){//??¨?????????????????????????????¨????????????
		if(prime[i] == 1){
			for(k = 2*i; k <= MAX_V; k += i){
				prime[k] = 0;//?´???°????????°????´???°??§??????
			}
		}
	}
	for(i = 2; i < MAX_V; i++){//?´????????????????
		sum[i + 1] = sum[i] + prime[i];//
	}
	while(scanf("%d", &n) == EOF){
		printf("%d\n", sum[n + 1]);
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <math.h>

using namespace std;

int prime[100000];
bool is_prime[1000000];

int sosuu(int n){
    int p=0;
    for (int i=0; i<=n; i++)
        is_prime[i]=true;
    is_prime[0]=is_prime[1]=false;
    for (int i=2; i<=n; i++) {
        if(is_prime[i]){
            prime[p++]=i;
            for (int j=i*2; j<=n; j+=i) {
                is_prime[j]=false;
            }
        }
    }
    return p;
}

int main(void){
    int n;
    cin>>n;
    cout<<sosuu(n)<<endl;
    return 0;
}

C++: #include <stdio.h>

int isprime(int n){
    for(int i = 2; i * i <= n; i++) {
        if(n % i == 0) return 0;  //素数でない
    }
    return 1; //素数である
}

int main() {
    int n;
    int ans[2] = {};
    while(scanf("%d", &n) != 0) {
        for(int i = n; i >= 5; i--) {
            if(isprime(i) == 1) {
                ans[0] = i;
                if(isprime(i - 2) == 1) {
                    ans[1] = i - 2;
                    break;
                }
            }
        }
        printf("%d %d", ans[0], ans[1]);
    }
}

C++: #include<stdio.h>

int main(void)
{
	int data,i,j,k=0,l=0,kai[100]={0},s[100000]={0};

	while(scanf("%d",&data) != EOF)
	{
		if(data<=1)
		   kai[k]=0;
		else
		{
			for(i=2;i<=data;i++)s[i]=i;

		    i=2;
			while(i*2<data)
			{
			  if(s[i] != 0)
			  {  
				j=2;
				while(j*i<=data)
				{
					s[j*i]=0;
					j+=1;
				}
			  }
			  i+=1;
			}

			
			for(i=2;i<=data;i++)
			{	
				if(s[i]!=0)
				{
					kai[k]+=1;
				}
			}
		}
		k+=1;
	}

  for(j=0;j<k;j++)
    printf("%d\n",kai[j]);
  return 0;
}

C++: #include <cstdio>
#include <iostream>
using namespace std;

bool nonprime[1000000];

int main(){
	long i,j,n;
	for(i=2;i<=999999;i++){
		for(j=2;i*j<=999999;j++) nonprime[i*j]=1;
	}
	while(scanf("%ld",&n)!=EOF){
		j=0;//j?????????????????¨?????????????????????
		for(i=2;i<=n;i++) if(!nonprime[i]) j++;
		cout << j << endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <iostream>

using namespace std;


int main(){
	int n;

	while(cin >> n){
		int ans=0;

		for(int number=2;number<=n;number++){
			int flag = 0;
			for(int i=2;i<number;i++){
				if(number%i==0){
					flag = 1;
					break;
				}
			}
			if(flag==0)ans++;
		}
		printf("%d\n",ans);
	}


	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long LL;
#define REP(i,N) for(int i = 0; i < (int)N; i++)

int main(){
	int max = 1000100;
	bool prime[1000100];
	int dp[1000000];
	prime[0] = prime[1] = false;
	int ret=0;
	memset(prime,true,sizeof(prime));
	memset(dp,0,sizeof(dp));
	int hako[30];
	memset(hako,0,sizeof(hako));
	REP(i,30) cin >> hako[i];
	for(int i=2;i<sqrt(max);i++)for(int j=i*2;j<max;j=j+i){
		prime[j] = false;
	}
	for(int i=1; i<max ;i++){
		dp[i]=dp[i-1];
		if(prime[i])dp[i]++;
	}
	REP(i,30)	cout << dp[hako[i]] << endl;
	return 0;
}

C++: #include <iostream>

using namespace std;

int main(){
	int n , ans = 1;

	while(cin >> n){
		ans = 1;
		if(n == 0) break;

		if(n <= 1){
			ans--;
		}

		for(int i = 2; i <= n; i++){
			if(i % 2 != 0 && 9 > i){
				cout << i << endl;
				ans++;

			}if(i >= 9){
				if(i % 2 != 0 && i % 3 != 0 && i % 5 != 0 && i % 7 != 0){
					cout << i << endl;
					ans++;
				}
			}
		}

		cout << ans << endl;
	}
	return 0;
}