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