#include <fstream>
#include <cmath>
#include <bitset>
using namespace std;
ifstream fin("ciur.in"); ofstream fout("ciur.out");
bitset <2000005> v;
int main()
{	int n,i,j,nr=1;
	fin>>n;
	int limita=(int)sqrt((double)n);
	for(i=4;i<=n;i+=2) v[i]=1;
	for(i=3;i<=limita;i+=2)
	if(v[i]==0)
	{	nr++;
		for(j=i*i;j<=n;j+=i) v[j]=1;
	}
	for(;i<=n;i+=2) if(v[i]==0) nr++;
	fout<<nr<<'\n';
	fout.close(); return 0;
}