#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n;
bool p[2000000];
int Number() {
  int i, j, nr = 1;
  for (i = 3; i <= n; i += 2) {
    if (p[i] == 0) {
      nr++;
      for (j = i + i + i; j <= n; j += i << 1) {
        p[j] = 1;
      }
    }
  }
  return nr;
}
int main()
{
    f>>n;
    g<<Number();
}