#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,k;
char v[2000001];
int main()
{
	f>>n;
	for (i=2;i<=n;i++)
		if (v[i]==0)
		{
			for (j=2*i;j<=n;j=j+i)
				v[j]=1;
			k++;
		}
	g<<k;
	f.close();
	g.close();
	return 0;
}