#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
const int N=2000001;
int main(){
	int n;
	f>>n;
	char c[N]={0};
	for (int i=2;i*i<=n;i++)
		if (c[i]==0)
			for(int j=i*i;j<=n;j+=i)
				c[j]=1;
	int nr=0;
	for(int i=2;i<=n;i++)
		if(c[i]==0) 
			nr++;
	g<<nr<<endl;
	
	return 0;}