#include <fstream>
#define NMax 2000005
using namespace std;

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

int c,a[NMax],i,j,n;

int main()
{f>>n;
 for (i=2;i*i<=n;i++)
   if (!a[i])
    for (j=2*i;j<=n;j+=i)
     a[j]++;
 for (i=2;i<=n;i++)
  if (!a[i]) c++;
 g<<c;
    return 0;
}