#include <fstream>

using namespace std;

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

int n, v[2000001], pr;

int main()
{
  fin >> n;
  for (int i = 3; i * i <= n; i++) {
    for (int j = i + i; j <= n; j += i)
      v[j] = true;
  }
  pr++;
  for (int i = 3; i <= n; i += 2)
    if (not v[i])
      pr++;
  fout << pr;
  return 0;
}