Go: package main

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

func main() {
    var limit = 1000000
    var root = 1000
    var isPrime [1000000]bool
    for i := 0; i < limit; i++ {
        isPrime[i] = true
    }
    isPrime[0] = false
    isPrime[1] = false
    for i := 2; i <= root; i++ {
        if isPrime[i] {
            for j := i * i;j < limit; j+=i {
                isPrime[j] = false
            }
        }
    }
    var primeCnt [1000000]int
    var cnt = 0
    for i := 0; i < limit; i++ {
        if isPrime[i] {
            cnt++
        }
        primeCnt[i] = cnt
    }

    var sc = bufio.NewScanner(os.Stdin)
    for sc.Scan() {
        n, _ := strconv.Atoi(sc.Text())
        fmt.Println(primeCnt[n])
    }
}

C++: #include <iostream>
#include <cmath>
#include <vector>
using namespace std;
// have you mooed today?
bool isprime(int& num)
{
    static int c;
    static int max;
    if(num == 1) return false;
    if(num == 2) return true;
    if(num % 2 == 0) return false;
    max = ceil(sqrt(num));

    for(c=3; c < max+1; c+=2)
        if(num % c ==0) return false;
    return true;
}

int main()
{
    int ans =0;
    int c;
    int buff;
    vector<int> prime;
    for(c=1;c<=999999;c++)
    {
        if(isprime(c)) ans++;
        prime.push_back(ans);
    }
    while(cin >> buff)
    {
        cout << prime[buff -1] << endl;
    }
    return 0;
}

C++: #include <cstdio>
#define MAX 1000000
#define SQRT 1000
#define TRUE 1
#define FALSE 0
using namespace std;

int is_prime[MAX];
int prime_count[MAX];

void solve() {
  int cnt = 0;
  for (int i = 0; i < MAX; i++) {
    is_prime[i] = TRUE;
  }
  is_prime[0] = is_prime[1] = 0;
  for (int i = 2; i < MAX; ++i) {
    if (is_prime[i] == TRUE) {
      if (i < SQRT) {
        for (int j = i * i; j < MAX; j += i) {
          is_prime[j] = FALSE;
        }
      }
      cnt++;
    }
    prime_count[i] = cnt;
  }
}

int main() {
  solve();
  int n;
  while (~scanf("%d", &n)) {
    printf("%d\n", prime_count[n]);
  }
}

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

using namespace std;

#define MAX_VALUE 1000000

int get_numprime( int num );

int main(void)
{
	int num;

	while(1)
	{
		cin >> num;
		if( cin.eof() ) break;
		int result = get_numprime( num );
		cout << result << endl;
	}

	return 0;
}

int get_numprime( int num )
{
	int numprime = 1; // 2はカウント済み

	bool erat[MAX_VALUE] = {0};

	for( int i = 0 ; i < num+1 ; i++ )
	{
		erat[i] = true;
	}
	erat[0] = false; erat[1] = false;
	for( int i = 2 ; i <= num ; i++ )
	{
		if( erat[i] )
		{
			for( int j = i*2 ; j <= num ; j+=i )
			{
				erat[j] = false;
			}
		}
	}
	for( int i = 3 ; i <= num ; i+=2 )
	{
		if( erat[i] ) numprime++;
	}

	return numprime;
}

C++: #include <bits/stdc++.h>
using namespace std;

bool prime(int n) {
	if (n < 2) return false;
	for (int i = 2; i < sqrt(n) + 1; i++) {
		if (n % i == 0) return false;
	}
	return true;
}

int main() {
	vector<int> v = vector<int>(1, 0);
	for (int i = 1; i < 1000000; i++) {
		if (prime(i)) {
			v.push_back(v.back() + 1);
		} else {
			v.push_back(v.back());
		}
	}
	int n;
	while (cin >> n) {
		if (n == 1) {
			cout << 0 << endl;
		} else {
			cout << v[n] + 1 << endl;	
		}
	}
}

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

int main(void){
        int n,i,j,c;
        int *p;
        while(scanf("%d",&n)!=EOF){
                c=0;
                if((p=(int *)malloc(sizeof(int)*(n+1)))==NULL){
                        return 1;
                }
                for(i=0;i<=n;i++){
                        p[i]=i;
                }
                for(i=2;i<=n;i++){
                        if(p[i]!=-1){
                                c++;
                                for(j=i;j<=n;j=j+i){
                                        p[j]=-1;
                                }
                        }
                }
                free(p);
                printf("%d\n",c);
        }
}

C++: #include<stdio.h>

int main(void)
{
	int data,i,j,k=0,l=0,kai=0,s[1000000]={0};

	while(scanf("%d",&data) != EOF)
	{
		if(data<=1)
		   kai=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+=1;
				}
			}
		}
		printf("%d",kai);
		kai=0;
	}

  return 0;
}

C++: //	created : 16/03/06
// 	autor   : Rp7rf
#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <set>
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
#define rep(i,a) for(int i = 0 ; i < a ; i ++)
#define loop(i,a,b) for(int i = a ; i < b ; i ++)
#define vi vector<int>
#define mp make_pair
#define pb push_back
#define MOD 1000000007
#define INF 1e9
#define MAX 999999
bool prime[MAX];
int cnt[MAX];

void init_prime(){
	rep(i,MAX){
		prime[i] = true;
		
	}
	prime[0] = prime[1] = false;
	int c = 0;
	rep(i,MAX){
		if(prime[i]){
			for(int j = i + i ; j < MAX ; j += i){
				prime[j] = false;
			}
			c++;
		}
		cnt[i] = c;

	}
}

int main(void){
	init_prime();
	int n ;
	while(cin>>n){
		cout<<cnt[n]<<endl;
	}
}

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

int main(){
 int n,i,j,x,counter;
 cin >> n;
 counter = 0;
 
 for (i = 1; i <= n; i++) {
   x = 0;
   
   for (j = 1; j <= i; j++) {
     if (i % j == 0) x++;
   }
   
   if (x == 2) counter++;
 }
 
 cout << counter << endl;
 
 return 0;
}

C++: #include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<string.h>
#include<math.h>
#include<cstring>
using namespace std;
#define NUM 1000000

int main(){
	long long int n;
	while(cin>>n){
		long long int i,j,a=0,p[NUM];
		for(i=0;i<NUM;i++)p[i]=0;
		for(i=2;i<1001;i++){
			if(p[i]==0){
				p[i]=2;
				for(j=2;j<=NUM/i;j++){
					p[j]=1;
				}
			}
		}
		for(i=2;i<=n;i++){
			if(p[i]==2){
				a++;
			}
		}
		cout<<a<<endl;
	}
    return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define all(c) ((c).begin()), ((c).end())
#define dump(c) cerr << "> " << #c << " = " << (c) << endl;
#define iter(c) __typeof((c).begin())
#define tr(i, c) for (iter(c) i = (c).begin(); i != (c).end(); i++)
#define REP(i, a, b) for (int i = a; i < (int)(b); i++)
#define rep(i, n) REP(i, 0, n)
#define mp make_pair
#define fst first
#define snd second
#define pb push_back

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<string> vs;
typedef pair<int, int> pii;

const int INF = 1 << 29;
const double EPS = 1e-10;

double zero(double d) {
    return d < EPS ? 0.0 : d;
}

template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
    return os << '(' << p.first << ',' << p.second << ')';
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &a) {
    os << '[';
    rep(i, a.size()) os << (i ? " " : "") << a[i];
    return os << ']';
}

// to avoid error on mingw
string toString(int i) {
    stringstream ss;
    ss << i;
    return ss.str();
}

const int MOD = 1000000007;
// a^k
ll fpow(ll a, ll k, int M) {
    ll res = 1ll;
    ll x = a;
    while (k != 0) {
        if ((k & 1) == 1)
            res = (res * x) % M;
        x = (x * x) % M;
        k >>= 1;
    }
    return res;
}

int main() {
    cout.setf(ios::fixed, ios::floatfield);
    cout.precision(8);
    ios_base::sync_with_stdio(false);

    const int MAX_N = 1000000;
    bool sieve[MAX_N];
    fill(sieve, sieve+MAX_N, true);
    sieve[1] = false;

    for(int i=2; i*i <= MAX_N; ++i) {
        for(int j=i*i; j < MAX_N; j += i) {
            sieve[j] = false;
        }
    }

    vi prime_num(MAX_N, 0);
    REP(i, 1, MAX_N){
        prime_num[i] = prime_num[i-1];
        if(sieve[i])
            prime_num[i]++;
    }

    int n;
    while(cin >> n) {
        cout << prime_num[n] << endl;
    }

    return 0;
}