//ciur cu bitset 
#include<iostream>
#include<fstream>
#include<bitset>
using namespace std;
bitset <2000001> v; //bitset <_size_> _nume_
int main ()
{
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int n,nr=1;
	fin>>n;
	for (int i=3;i<=n;i+=2)
	{
		if (v[i]==0)
		{
			for (int j=i+i;j<=n;j+=i)
				v[j]=1;
			nr++;
		}
	}
	fout<<nr;
	fin.close(); fout.close();
	return 0;
}