#include <iostream>
#include <cmath>
#include <fstream>
using namespace std;
void ciur(int v[], int n, int &nr)
{
  int i = 2, j;
  while (i <= n) {
    if (v[i] != -1) {
      ++nr;

      for (j = i + i; j <= n; j += i)
        v[j] = -1;
    }
    ++i;
  }
}

int main()
{
  int n, i, nr = 0;
  ifstream fin("ciur.in");
  fin >> n;
  int v[n * 2] = {};

  ofstream fout("ciur.out");

  ciur(v, n, nr);
  fout << nr;
  return 0;
}