#include<fstream>

using namespace std;

const int N=2000001;

int main()
{
	ifstream strat("ciur.in");
	ofstream up("ciur.out");
	int n;
	strat>>n; 
	char c[N]={0};
	for (int i=2; i*i<=n ; ++i)
		if (c[i]==0)
			for (int j=i*i ; j<=n; j+=i)
				c[j]=1;
	int nr=0;
	for (int i=2;i<=n;++i)
		if (c[i]==0)
			++nr;
	up<<nr<<endl;
	strat.close();
	up.close();
	return 0;
}