Go: package main

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

var sc = bufio.NewScanner(os.Stdin)

func main() {
	var primeCount int
	for sc.Scan() {
		input := nextInt()
		for i := 0; i <= input; i++ {
			if IsPrime(i) {
				primeCount++
			}
		}
		fmt.Printf("%d\n", primeCount)
		primeCount = 0
	}
}

func IsPrime(num int) bool {
	switch {
	case num == 2:
		return true
	case num < 2 || num%2 == 0:
		return false
	}
	sqrt := math.Sqrt(float64(num))
	for i := 3; i <= int(sqrt); i += 2 {
		if num%i == 0 {
			return false
		}
	}
	return true
}

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

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

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

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

int main()
{
	int n;
	while (cin >> n)
	{
		int ans = 0;
		for (int i = 2; i <= n; i++)
		{
			if (IsPrime(i)) ans++;
		}
		cout << ans << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <math.h>
#include <string>
#include <string.h>
#include <stack>
#include <algorithm>
#include <stdio.h>
using namespace std;

bool a[1000000];

int main()
{
	int n;
	while (cin >> n)
	{
		if (n == 1)
		{
			cout << 0 << endl;
		}
		else
		{
			memset(a, false, sizeof(a));

			int cnt = 0;
			for (int i = 2; i <= n; i++)
			{
				if (a[i] == false)
				{
					cnt++;
					for (int j = 1; i * j <= n; j++)
					{
						a[i * j] = true;
					}
				}
			}
			cout << cnt << endl;
		}
	}

	return 0;
}

C++: /*http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0009&lang=jp*/

#include <iostream>

#define MAX 999999

using namespace std;

int main()
{
    int n;
    static int num_prime[MAX+1];
    static bool not_prime_flag[MAX+1];

    for (int i = 2; i < MAX+1; ++i) {
        if(!not_prime_flag[i]){
            for (int j = 2; i*j < MAX+1; ++j) {
                not_prime_flag[i*j] = true;
            }
        }
        num_prime[i]=num_prime[i-1]+!not_prime_flag[i];
    }
    while (cin>>n){
        cout<<num_prime[n]<<endl;
    }
    return 0;
}

C++: #include<iostream>
using namespace std;
int main(){
	int n, cnt;	

	while(cin >> n){
		bool prime[1000000] = {false};
		prime[1] = true;
		
		// ??¨??????????????????????????????
		for(int j = 2; j*j <= n; j++){
			if(prime[j] == false){
				for(int k = j; k*j <= n; k++){
					prime[j*k] = true;
				}
			}
		}
		cnt = 0;
		for(int i = 1; i <= n; i++){
			if(prime[i] == false) cnt++;
		}
		
		cout << cnt << endl;
	}
}

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

int main(){
  int a;
  int i, j;
  int past=1, a_sqrt;
  int count;
  bool chk[1000000];

  for(i=1; i<1000000; i++) chk[i]=true;
  while(cin>>a){
    count=0;
    if(past>=a){
      for(i=1; i<=a; i++){
        if(chk[i]) count++;
      }
      printf("%d\n", count);
    }
    else {
      printf("%d\n", count);
    }
  }

  return 0;
}

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

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(const std::vector<int> src){
	std::vector<int> result,tmp(src);
	while(!tmp.empty()){
		int n(tmp[0]);
		result.push_back(n);
		Mod mod(n);
		std::vector<int>::iterator it= std::remove_if( tmp.begin(), tmp.end(), mod );
		tmp.erase(it,tmp.end());
	}
	return result;
}
static int const MAX(1000000);

int main(int,char**){
	std::vector<int> vec;
	vec.reserve(MAX-MAX/2-MAX/3-MAX/5+MAX/6+MAX/10+MAX/15-MAX/30+3);
	for(int i(3);i<=MAX;i+2){
		if(i!=3 && i%3==0) continue;
		if(i!=5 && i%5==0) continue;
		vec.push_back(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 <stdio.h>

int isprime(int n){
    for(int = 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 <iostream>
using namespace std;

int main()
{
	int n, x = 0;
	int countdata[1000];
	while (cin >> n) {
		int count = 0;
		for (int a = 2; a <= n; a++) {
			if (a % 2 != 0 && a % 3 != 0 && a % 5 != 0 && a % 7 != 0) {
				count++;
			}
		}
		countdata[x] = count+4;
		x++;
	}
	for (int a = 0; a < x; a++) {
		cout << countdata[a] << endl;
	}
}

C++: #include <cstdio>
#define max_n 999999
int prime[max_n];
bool is_prime[max_n+1];
int main(){
    for(int i=0; i<max_n; i++){
        is_prime[i]=true;
    }
    int p = 0;
    is_prime[1]=false;
    is_prime[0]=false;
    for(int i=2;i<max_n;i++){
        if(is_prime[i]){
            prime[p++] = i;
            for(int j=2*i;j<max_n;j+=i)is_prime[j]=false;
        }
    }

    while(true){
        int n;
        scanf("%d",&n);
        int ans = 0;
        for(int i =0; i<max_n; i++){
            if(prime[i]>n){
                ans = i;
                break;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<map>
#include<queue>
#include<cmath>
#include<stack>
#include<vector>
#include<cstdio>
#define MAXN 2555
#define INF 0x3f3f3f3f
#define v first
#define b second
using namespace std;
const int N = 1000000;
bool prime[N];
int p[N],tot=0;
void init(){
    for(int i = 2; i < N; i ++) prime[i] = true;
    for(int i = 2; i < N; i++){
        if(prime[i]) p[tot ++] = i;
        for(int j = 0; j < tot && i * p[j] < N; j++){
            prime[i * p[j]] = false;
            if(i % p[j] == 0) break;
        }
    }
}

int main()
{
   init();
   int n;
   while(scanf("%d",&n)==1)
   {
      int sum=0;
      for(int i=0;i<tot;i++)
      {
         if(p[i]<=n)
            sum++;
         else break;
      }
      cout<<sum<<endl;
   }
   return 0;
}

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

int main(void) {

	//0005
	/*
	int a, b, G, R, L, r;
	while (cin >> a >> b) {
		R = a;
		L = b;
		int tmp;
		if (b > a) {
			tmp = a;
			a = b;
			b = tmp;
		}
		while (1) {
			r = a%b;
			if (r == 0)break;
			a = b;
			b = r;
		}
		G = b;
		R = R / G;
		L = L / G;
		cout << G << " " << R*L * G << endl;
	}
	*/
	//0006
	/*
	string name;
	cin >> name;
	int L = name.size();
	string Ans;
	for (int i = 0; i < L; i++) {
		Ans += name.substr(L-i-1, 1);
	}
	cout << Ans << endl;
	*/
	//0007
	/*
	int Dept = 100000;
	int week;
	cin >> week;
	for (int i = 0; i < week; i++) {
		Dept = Dept * 1.05;
		if (Dept % 1000 == 0) {
			Dept = (Dept / 1000);
		}
		else {
			Dept = (Dept / 1000 + 1);
		}
		Dept = Dept * 1000;
	}
	cout << Dept << endl;
	*/
	//0008
	/*
	int a, b, c, d;
	int n;
	int count[51];
	for (int i = 0; i < 51; i++) {
		count[i] = 0;
	}
	for (a = 0; a < 10; a++) {
		for (b = 0; b < 10; b++) {
			for (c = 0; c < 10; c++) {
				for (d = 0; d < 10; d++) {
					count[a + b + c + d]++;
				}
			}
		}
	}
	while (cin >> n) {
		cout << count[n] << endl;
	}
	*/
	int n;
	while (cin >> n) {
		if (n == 1) {
			cout << 0 << endl;
			break;
		}
		int count = 1;
		for (int i = 2; i <= n; i++) {
			for (int j = 2; j < i; j++) {
				if (i%j == 0)break;
				if (j == i-1)count++;
			}
		}
		cout << count << endl;
	}
	return 0;
}