#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
using namespace std;
static const double EPS = 1e-5;
typedef long long ll;
#define FOR(i,n) for(i=0;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)

int p[1000010];

int main(){
	p[0]=p[1]=1;
	rep(i,1000000){
		if(p[i]==0)
			for(int j=2*i;j<1000000;j+=i)
				p[j]=1;
	}
	int n;
	cin>>n;
	int r=0;
	rep(i,n)
	if(p[i]==0)r++;
	cout<<r<<endl;
	return 0;
}