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

using namespace std;

int main() {
ifstream in("ciur.in");
ofstream out("ciur.out");
bool a[2000001];
int nr=0, n, i, j;
in>>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++;
out<<nr;
in.close();
out.close();
return 0;
}