#include <fstream.h>
long n,i,j,np;
char v[2000001];
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int main ()
{
	fin>>n;
	for (i=3;i<=n;i=i+2)
		if (v[i]==0)
		{
			np++;
			for (j=i+i;j<=n;j=j+i)
				v[j]=1;
		}
fout<<np+1;
return 0;
}