Go: package main

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

var sc = bufio.NewScanner(os.Stdin)

func main() {
	for sc.Scan() {
		input := nextInt()
		fmt.Println(IsPrime(input))
	}
}

func IsPrime(num int) int {
	eratos := make([]bool, num+1)
	c := 0
	for i := 2; i < len(eratos); i++ {
		if eratos[i] == false {
			c++
			eratosCalc(i, eratos)
		}
	}
	return c
}

func eratosCalc(primeNum int, eratos []bool) {
	for i := primeNum * primeNum; i < len(eratos); i += primeNum {
		eratos[i] = true
	}
}

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

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

C++: 
//  test.cpp

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <string>
#include <algorithm>

using namespace std;


int main(){
    long j,s[1000000],d=1,i,n,k;
    
    for(i=2;i<1000000;i++){
        if(s[i]==0){
            
            for(j=2;j*j<i;j+=2){
                if(j%i==0)
                    break;
                if(j==2)
                    j=1;
            }
            
            if(j*j>=i){
                d++;
                for(k=2;k*i<1000000;k++){
                    s[k*i]=-1;
                }
            }
        }
        s[i] = d;
    }
    
    while(EOF != scanf("%ld",&n)){
        printf("%ld\n",s[n]-1);
    }
    
    
    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <cmath>
//ranker
using namespace std;

#define REPS(i, a, n) for (int i = (a); i < (n); ++i)
#define REP(i, n) REPS(i, 0, n)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (int i = (a); i >= n; --i)
#define DEP(i, n) DEPS(i, n, 0)

using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using pis = pair<int, string>;
using psi = pair<string, int>;
using D = double;


const int Max=10000000;
bool prime[Max];
int main(void){
    int in;
    for(int i=0;i<Max;i++)prime[i]=true;
    prime[1]=false;
    for(int i=2;i<Max;i++){
        if(prime[i]){
            for(int s=i*2;s<=Max;s+=i)prime[s]=false;
        }
    }
    while(cin>>in){
        int cnt=0;
        for(int i=1;i<=in;i++){
            if(prime[i])cnt++;
        }
        cout << cnt << "\n";
    }
    return 0;
}

C++: #include <iostream>
using namespace std;
int main() {
	bool isprime[1000000];
	for (int i = 0; i < 1000000; i++)
		isprime[i] = 1;
	for (int i = 2; i < 1000; i++) {
		if (!isprime[i]) continue;
		for (int j = i * i; j < 1000000; j += i)
			isprime[j] = 0;
	}
	int n;
	while (cin >> n) {
		int ans = 0;
		for (int i = 2; i <= n; i++)
			if (isprime[i])
				ans++;
		cout << ans << endl;
	}
}

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

using namespace std;

int main()
{
	vector<long long int>D(1000001 , 1);
	D[0] = 0;
	D[1] = 0;
	for(long long int i = 2; i <= sqrtl(1000001); i++)
	{
		if(D[i])
		{
			long long int j = 2;
			while(i*j < 1000001)
			{
				D[i*j] = 0;
				j++;
			}
		}
		D[i] += D[i - 1];
	}
	long long int n;
	while(cin >> n)cout << D[n] << endl;
	return 0;
}

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

int arr[1000000];

int main()
{
	int x, cnt, j, i = 3;
	arr[2] = 1;
	for (; i < 1000000; ++i) {
		cnt = 1;
		for (j = 2; j <= sqrt(i); ++j) {
			if (i%j == 0) {
				arr[i] = arr[i - 1];
				--cnt;
				break;
			}
		}
		arr[i] = arr[i - 1] + cnt;
	}
	while (cin >> x) {
		cout << arr[x] << endl;
	}
	return 0;
}

C++: #include<stdio.h>
int a[1000001];

int Func(int n) {
	if (n == 0)return 0;
	else return a[n] + Func(n - 1);
}

int main() {
	a[0] = 0;
	a[1] = 0;
	a[2] = 1;
	for (int i = 3; i <= 1000000; i++) {
		if (i % 2 == 0)a[i] = 0;
		else {
			int h = 1;
			for (int j = 3; j*j <= i && h == 1; j += 2) {
				if (i%j == 0)h = 0;
			}
			a[i] = h;
		}
	}
	int n;
	while (~scanf("%d", &n)) {
		printf("%d\n", Func(n));
	}
}

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

int main()
{
	int prime[1000000];
	bool is_prime[1000000];
	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 count = 0;
	for (int i = 0; i < 1000000; i++) {
		if (is_prime[i])
			count++;
		prime[i] = count;
	}
	int n;
	while (cin >> n) {
		cout << prime[n] << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<math.h>
#define MAX (1000000)
using namespace std;

int N;
int array[MAX];
int count = 0;
int main(){
	cin >> N;
	
	for(int i=0; i < N; i++){
		array[i]=1;
	}
	
	for(int i=2; i < sqrt(N); i++){
		for(int j=1; i*j < N; j++){
			array[i*j] = 0; 
		}
	}
	
	for(int i=0; i < N; i++){
		if(array[i] == 1){
			count++;
		}
	}
	cout << count << endl;
	
	return 0;
}

C++: #include<iostream>

using namespace std;

int n;
int prime[1000000];
int checked[1000000];
int primesum[1000000];
int result[30];
int datasets;

int main()
{
	prime[0] = 0;
	prime[1] = 0;
	prime[2] = 1;
	primesum[0] = 0;
	primesum[1] = 0;
	primesum[2] = 1;
	
	for(int a = 3;a<1000000;a++)
	{
		if(checked[a] == 0)
		{
			prime[a] = 1;
			checked[a] = 1;
			for(int b = 2;b<a;b++)
			{
				if(a%b==0)
				{
					prime[a] = 0;
					break;
				}
			}
			if(prime[a] == 1)
			{
				for(int c = 2*a ;c<1000000;c+=a)
				{
					checked[c] = 1;
				}
			}
		}
		primesum[a] = primesum[a-1]+prime[a];
	}
	
	while(cin >> n)
	{
		cout << primesum[n] << endl;
	}

	return 0;
}

C++: #include<iostream>

using namespace std;

int main(){
	int n;
	int p[1000000] = { 1 };
	int ans[1000000] = { 0 };
	p[0] = 0;
	p[1] = 0;

	for (int i = 2; i*i < 1000000; i++){
		if (p[i]){
			for (int j = 2 * i; j < 1000000; j += i){
				p[j] = 0;
			}
		}
	}

	for (int i = 0; i < 1000000; i++){
		ans[i] += p[i];
	}

	while (cin >> n)
		cout << ans[n] << endl;

}

C++: #include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <list>
#include <numeric>
#include <utility>
#include <ctime>
#define INF 100000000
#define LINF 9000000000000000000
#define mod 1000000007
 
#define rep(i,n) for(int i=0;i<int(n);i++)
#define REP(i,a,b) for(int i=(a);i<int(b);i++)
#define all(x) (x).begin(),x.end()
#define pb push_back
#define mp make_pair
#define MOD(x) (x%(mod))
 
using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef pair<int,int> pi;
 
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
bool debug=false;

/*---------------------------------------------------*/

int n;
int weight[30],max_weight[30];

bool DFS(int now,int cnt,bool used[]){
  //cout<<"DEBUG: "<<now<<" "<<cnt<<endl;
  bool ok=false;
  if(cnt==n)return true;
  rep(i,n){
    if(!used[i]&&now+weight[i]<=max_weight[i]){
      used[i]=true;
      ok=DFS(now+weight[i],cnt+1,used);
      if(ok)return true;
      used[i]=false;
    }
  }
  return false;
}

int main(){
  bool used[26];
  while(cin>>n){
    if(n==0)break;
    rep(i,n)cin>>weight[i]>>max_weight[i];
    bool ok=false;
    rep(i,n){
      used[i]=true;
      if(DFS(weight[i],1,used))ok=true;
      used[i]=false;
    }
    if(ok)cout<<"Yes"<<endl;
    else cout<<"No"<<endl;
  }
}

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

int pn[1000002];

int solve (int n) {
  int Count = 0;
  memset(pn, 0, n);
  pn[0] = pn[1] = 1;
  for (int i = 2; i <= n; i++) if (!pn[i]) for (int j = 2; i * j <= n; j++) pn[i * j] = 1;
  Count = count(pn, pn+n+1, 0);
  return Count;
}
	

int main (void) {
  int n;
  cin.tie(0);
  while (scanf("%d", &n) != EOF) {
    cout << solve(n) << endl;
  }
  return 0;
}