#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

#define MAXSIZE 2000000/2/8+1
char p[MAXSIZE];

///(p[i>>3]&(1<<(i&7))) == 0 if 2*i + 1 is prime

int getTheNumber(int n) {
  int i, j, nr = 1;
  for (i = 1; ((i * i) << 1) + (i << 1) <= n; i += 1) {
    if ((p[i >> 3] & (1 << (i & 7))) == 0) {
      for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1) {
        p[j >> 3] |= (1 << (j & 7));
      }
    }
  }
  for (i = 1; 2 * i + 1 <= n; ++i)
       if ((p[i >> 3] & (1 << (i & 7))) == 0)
           nr++;
  return nr;
}

int main()
{
    int n;
    f>>n;
    g<<getTheNumber(n)<<"\n";
    return 0;
}