#include <fstream>
using namespace std;

const int N=2000005;
bool c[N];

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

void ciur()
{
	c[0]=c[1]=true;
	for (int i=2;i*i<N;i++)
		if (!c[i])
			for (int j=i*i;j<N;j+=i)
				c[j]=true;
}
	
int main()
{
	ciur();
	int n,nr=0;
	in>>n;
	for (int i=1;i<=n;i++)
		if(!c[i])
			nr++;
	out<<nr<<"\n";
	return 0;
}