#include <fstream>
#define L 2000001
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char ciur[L + 1];
int main(){
  int n, i, d;
  fin >> n;
  for (d = 2; d * d <= L; d++)
    if (ciur[d] == 0)
      for (i = d * d; i <= L; i += d)
        ciur[i] = 1;
  d = 0;
  for (i = 2; i <= n; i++)
    d = d + 1 - ciur[i];
  fout << d << "\n";
  return 0;
}