#include<fstream>
using namespace std;
const int N=2000001;
int main()
{
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	int n;
	in>>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;
	out<<nr<<"\n";
	in.close();
	out.close();
	return 0;
}