Go: package main

import (
        "fmt"
)

const MAX int = 1000000
var primes [MAX]int

func main() {
        Init()
        var n, cnt int
        for {
                _, err := fmt.Scanf("%d", &n)
                if err != nil {
                        break
                }
                cnt = 0
                for i := 2; i <= n; i++ {
                        cnt += primes[i]
                }
                fmt.Printf("%d\n", cnt)
        }
}

func Init() {
        for i := 0; i < MAX; i++ {
                primes[i] = 1
        }
        primes[0] = 0
        primes[1] = 0
        Soe()
}

func Soe() {
        for i := 2; i < MAX; i++ {
                if primes[i] > 0 {
                        for j := i*2; j < MAX; j+=i {
                                primes[j] = 0
                        }
                }
        }
}

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

	bool is_prime[1000000];
	int n_prime[1000000];
int main()
{
	
	is_prime[0]=is_prime[1]=false;
	for(int i=2; i<1000000; i++){
		is_prime[i]=true;
	}
	
	for(int i=2; i*i<1000000; i++){
		if(is_prime[i]){
			for(int j=i*i; j<1000000; j+=i){
				is_prime[j]=false;
			}
		}
	}


	int cnt=0;
	for(int i=0; i<1000000; i++){
		if(is_prime[i]){
			cnt++;
		}
		n_prime[i]=cnt;
	}
	while(true){
		int n;
		cin>>n;

		if(cin.eof())
			break;
	
		cout<<n_prime[n]<<endl;
	}
	
	return 0;
}

C++: #include<iostream>
#include<cstdio>
using namespace std;
int main()
{
	int n,m,j,i,s;
	bool yes;
	while(cin>>n)
	{
		s=0;
		for(i=2;i<=n;i++)
		{
			if(i==2||i==3||i==5||i==7)s++;
			else if(i%2!=0&&i%3!=0&&i%5!=0&&i%7!=0)s++;
		}
		cout<<s<<endl;
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
bool Eratosthenes[999999+30];

int main()
{
    int n,pos;
    int c;

    while(cin>>n)
    {
        c=0;
        Eratosthenes[1]=false;

        for(int i=2; i<=n; i++) Eratosthenes[i]=true;
        for(int i=2; i<=n; i++)
        {
            if(Eratosthenes[i]==true)
            {
                pos=2*i;
                while(pos<=n)
                {
                    Eratosthenes[pos]=false;
                    pos=pos+i;
                }
            }
        }
        for(int i=1; i<=n; i++)
        {
            if(Eratosthenes[i]==true)
                c++;
        }
        cout<<c<<endl;

    }
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <functional>
#define F first
#define S second
using namespace std;
typedef pair<int, int> P;
const int INF = 1 << 30, Array = int(1e6);

int main(){

  int n, i, j, maxin = 2;
  bool jud;
  vector <int> vec;

  while(cin >> n){
    if(maxin < n){
      for(i = maxin;i <= n; i++){
        jud = 0;
        for(j = 0;  j < vec.size() ; j++){
          if(vec[ j ] * vec[ j ] > i) break;
          if( !( i % vec[ j ] ) ){
            jud = 1;
            break;
          }
        }
        if(!jud)
          vec.push_back( i );
      }
      maxin = n;
    }
    cout << upper_bound(vec.begin(), vec.end(), n) - vec.begin()   <<endl;
  }
}

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

using namespace std;

#define LOG(...) fprintf(stderr, __VA_ARGS__)
//#define LOG(...)
#define FOR(i, a, b) for(int i=(int)(a); i<(int)(b); ++i)
#define REP(i, n) for(int i=0; i<(int)(n); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define EXIST(s, e) ((s).find(e)!=(s).end())
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define SQ(n) (n) * (n)

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int MAX_VALUE = 1000007;
bool prime[MAX_VALUE];

int main() {
  FOR(i, 2, MAX_VALUE){
    if(prime[i]) continue;
    for(int j = i * 2; j<MAX_VALUE; j+=i)
      prime[j]=true;
  }

  int n;
  while(cin >> n) {
    int cnt = 0;
    FOR(i, 2, n + 1){
      if (!prime[i]) cnt++;
    }
    cout << cnt << endl;
  }
}

C++: #include <iostream>
using namespace std;
void solve(int n);

int main() {
	int n;
	while (cin >> n) {
		if (n<=1) cout << 0 << endl;
		solve(n);
	}
	return 0;
}
void solve(int n) {
	int prime[n];
	int i=0;j=0;
	for (i=2; i<=n; i++) {
		prime[j] = i;
		j++;
	}

	int p;
	for (i=0; i<n; i++) {
		p = prime[i];
		if (p == -1) continue;
		
		for (int k=i+1; k<n; k++) {
			if (prime[k]%p == 0)
				prime[k] = -1;
		}
	}
	int count = 0;
	for (int i=0; i<n; i++)
		if (prime[i] != -1) count++;
	cout << count << endl;
}

C++: #include <stdio.h>
#include <string.h>
int main(void){
    int n=9999,a,b,c;
    char x[1000000];
    memset(x,0,sizeof(x));
    for(a=2,c=0;a<=n;a++){
        if(x[a]){x[a]=c;continue;}
        x[a]=++c;
        for(b=a*2;b<=n;b+=a)x[b]=-1;
    }
    while(~scanf("%d",&n)){
        printf("%d\n",x[n]);
    }
    return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define M_PI 3.14159265358979
#include <iostream>
#include <stdio.h>
#include <string>
#include <math.h>
#include<iomanip>
#include<vector>
#include<cmath>
#include <algorithm>

using namespace std;

int yakusuu(int i){
	int counter=0;
	for (int j = 1; j <= i; j++){
		if (i%j == 0) counter++;
	}
	return counter;
}


int main()
{
	int n;
	
		
		while (scanf("%d",&n)!=-1)
		{
			int counter1 = 0;
			for (int i = 0; i <= n; i++)
			{
				if (yakusuu(i) == 2) counter1++;
			}

				cout << counter1 << endl;
		}
		
		
	return 0;
}

C++: #include <iostream>
using namespace std;
 
 bool IsPrime(int n){
    for(int i=2;i*i<=n;i++){
        if(n%i == 0){return false;}
    }
    return true;
}
 
 
int main(void) {
    int n;
 
    while(cin >> n){
    	for(i=2;i<=n;i++){
 　　		if(IsPrime(i)) count++;
 　	}
    	cout << count << endl;
    }
    
    return 0;
}

C++: #include <iostream>
#include <cmath>
using namespace std;
int prime(int);
int main(){
    int a,sum;
    int b[999999];
    b[0]=0;
    for(int i=1;i<999999;i++){
        b[i]=prime(i+1);
    }
    while ( cin >> a){
        sum =0;
        for (int i=1;i<a;i++){
            sum +=b[i];
        }
        cout << sum << endl;
    }
}
int prime(int x){
    if(x==1)
        return 0;
    if(x==2)
        return 1;
    for (int i=2;i<=sqrt(x)+1;i++){
        if(x%i==0)
            return 0;
    }
    return 1;
}

C++: #include <iostream>

using namespace std;

int main(void){
	int val;
	while(cin >> val)
		cerr << val << endl;

	return 0;
}

C++: #include <stdio.h>
#include <string>
#include <iostream>
#include <math.h>

using namespace std;

int sosuu(int n);

int main(){
    int n=0;
    int num=0;
    int a[30][2]={0};
    int max=0;
    while(scanf("%d",&n)!=EOF){
        if(max<n){
            max=n;
        }
        a[num][0]=n;
        num++;
    }
    
    int b[max];
    int c[max];
    int so=0;
    for(int i=0; i<=max; i++){
        b[i]=i;
    }
    b[1]=0;
    
    for(int i=2; i<sqrt(max); i++){
        for(int j=i+1; j<=max; j++){
            if(j%i==0){
                b[j]=0;
            }
        }
    }
    
    for(int i=0; i<=max; i++){
        if(b[i]!=0){
            c[so]=i;
            so++;
        }
    }
    
    
//    for(int j=0; j<num; j++){
//        cout<<a[j][0]<<"\n";
//    }
//    
//    for(int j=0; j<=so; j++){
//        cout<<c[j]<<"\n";
//    }
    
    
    
    
    for(int i=0; i<num; i++){
        for(int j=0; j<so; j++){
            if(c[j]<=a[i][0]){
                a[i][1]++;
            }else{
                j=so;
            }
        }
    }

    
    for(int j=0; j<num; j++){
        cout<<a[j][1]<<"\n";
    }
    
}