using namespace std;
#include<fstream>

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