#include<cmath>
#include<fstream>
using namespace std;
ifstream fin("date.in");
ofstream fout("date.out");
int n,i,j,h,k,ok;
char v[2000001];
int main(){
	fin>>n;
	for(i=2;i<=n;i++)
		if(v[i]==0){
			k++;
			for(j=i+i;j<=n;j=j+i)
				v[j]=1;
		}
	fout<<k;
	return 0;
}