using namespace std;
#include<fstream>

int main ()
{
	int N, i, j, nr=0;
	bool phi[2000005];
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	in>>N;
	for(i=2;i<=N;i++)
		phi[i]=1;
	for(i=2;i<=N;i++)
	{
		if(phi[i])
		{
			nr++;
			for(j=2*i;j<=N;j+=i)
				phi[j]=0;
		}
	}
	out<<nr;
	in.close();out.close();
	return 0;
}