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