#include <fstream>
#include <cmath>
using namespace std;

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

int t[2000005], n, i, j, x = 0;

int main()
{
  in >> n;
  t[0] = t[1] = 1;
  for (i = 2; i <= int(sqrt(n)); i ++)
      if (t[i] == 0)
         for (j = 2; j <= n/i; j ++)
             t[i*j] = 1;
  for (i = 1; i <= n; i ++)
      if (t[i] == 0)
         x ++;
  out << x;
  return 0;
}