#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

int n;
vector<bool > v;

void read()
{
	fstream f("ciur.in", ios::in);
	f>>n;
	v.resize(n+1, 1);
	f.close();
}

void solve()
{
	read();
	int i, j;
	for (i=2; i<=n; ++i)
		if (v[i]==1)
			for (j=2; i*j<=n; ++j)
				v[i*j]=0;

	int nr_sol=0;

	for (i=2; i<=n; ++i)
		if (v[i]==1)
			++nr_sol;
	fstream g("ciur.out", ios::out);
	g<<nr_sol;
	g.close();
}

int main()
{
	solve();
	return 0;
}