#include<fstream>
using namespace std;

ifstream is("ciur.in");
ofstream os("ciur.out");

int main()
{
	unsigned char prim[2000000];
    int i,j,n;
    int nrprime=0;
	is>>n;
	prim[0]=prim[1]=0;
	for(i=2;i<=n;i++) prim[i]=1;
	for(i=2;i<=n;i++)
		if(prim[i]==1)
		{
			nrprime++;
			for(j=i+i;j<=n;j=j+i)
				prim[j]=0;
		}
    os<<nrprime;
    return 0;
}