#include<fstream>
#define dmax 2000002
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,nr;
bool sir[dmax];
int main()
{	int i,j;
	in>>n;
	in.close();
	for(i=2;i<=n;i++)
		sir[i]=1;
	for(i=2;i<=n;i++)
		if(sir[i]==1)
		{	nr++;
			for(j=i+i;j<=n;j+=i)
				sir[j]=0;
		}
	out<<nr;
	out.close();
	return 0;
}