#include<fstream>

#define dim1 2000001

using namespace std;


char a[dim1];
long n;

void ciuru(){
	ofstream g("ciur.out");
	long  nr = 0;
	a[0]=a[1]=1;
	for(long p = 2; p < n; p++) {
		if(a[p]==0) {
			nr++;
			for(long i=2*p;i < dim1; i+=p)
				a[i]=1;
		}
	}
	g << nr;
	g.close();
}

void afisare()
{

	
	
}

int main(){
	ifstream f("ciur.in");
	f >> n;
	ciuru();
	return 0;

}
//---------------------------------------------------------------------------