#include <fstream>
using namespace std;
#define dmax 2000001
bool a[dmax];

ifstream cin("ciur.in");
ofstream cout("ciur.out");

void ciur(){
	int i, j, x;
	a[0]=a[1]=1;
	x=dmax/2;
	for (i=2;i<=x;i++) a[2*i]=1;
	for (i=3;i*i<=dmax;i+=2){
		x=dmax/i;
		for (j=2;j<=x;j++)
			a[j*i]=1;
	}
}

int main(){
	ciur();
	int n, k=1, i;
	cin>>n;
	for (i=3;i<=n;i+=2)
		if (a[i]==0) k++;
	cout<<k;
	cin.close();
	cout.close();
	return 0;
}