#include<fstream>
#include<vector>
#define N 2000100
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
vector<int> pr;
int lp[N],n;
int main ()
{
	f>>n;
	for(int i=2;i<=n;++i)
	{
		if(lp[i]==0)
		{
			lp[i]=i;
			pr.push_back(i);
		}
		for(int j=0;j<(int)pr.size()&&pr[j]<=lp[i]&&i*pr[j]<=n;++j)
			lp[i*pr[j]]=pr[j];
	}
	g<<pr.size();
	return 0;
}