#include<fstream>
using namespace std;

const int N=2000001;
bool c[N];

ifstream in ("ciur.in");
ofstream out("ciur.out");

int main()
{
	int n;
	in>>n;
	for(int i=2; i*i<=n; ++i)
		if(!c[i])
			for(int j=i*i; j<=n; j+=i)
				c[j]=true;
	int nr=0;
	for(int i=2;i<=n;++i)
		if(!c[i])
			++nr;
	out<<nr;
	return 0;
}