#include <fstream>
#include <math.h>

using namespace std;

int main() {
ifstream fin("ciur.in ");
ofstream fout("ciur.out");
bool a[2000001];
int nr=0, n, i, j;
fin>>n;
for (i=2;i<=n;i++)
  a[i]=1;
for (i=2;i<=sqrt(n);i++)
 if (a[i])
  for (j=i;j<=n/i;j++)
     a[i*j]=0;
for (i=2;i<=n;i++)
  if (a[i]) nr++;
fout<<nr;
fout.close();
return 0;
}