#include<fstream>
using namespace std;
ifstream fi("ciur.in");
ofstream fo("ciur.out");
long long int n,i,j,k=1;
char v[20000005];
int main(){
	fi>>n;
	for(i=3;i<=n;i+=2)
	   v[i]=1;
	   for(i=3;i<=n;i+=2){
	   	if(v[i]){
	   		k++;
	   		for(j=i*i;j<=n;j=j+i)
	   		   v[j]=0;
		   }
	   }
	   fo<<k<<" ";
	   fi.close();
	   fo.close();
	   return 0;
}