#include<fstream>
#define dim 2000002
using namespace std;
char prim[dim];
long long i,j;
long long n;
long long nrprime;
ifstream f("eratostene.in");
ofstream g("eratostene.out");
int main()
{
	f>>n;
	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;
		}
		g<<nrprime;
		return 0;
}